The Best Sliding Door System

Sky House Design Centre is home to a large range of slim framed aluminium sliding door systems, all on show throughout our building. That, paired with the expert architects and developers that visit us on a weekly basis, places us in a unique position to be able to be an excellent and objective third-party verifier and assessor of slim sliding doors across the market.  

We are often asked by our visitors “what is the difference between this one and that one?” or “I’ve had a cost for this sliding door, how does this one compare?”. So we thought it was about time we brought together all our expertise, experiences, knowledge and technical know-how to create this guide to help you to pick the right slim sliding glass door for your project.  

This article is only looking at slim framed external aluminium systems. We are not looking at steel and timber sliders and are only looking at external systems with with sightlines no larger than 26mm. Anything larger than 26mm would no longer be classed as ‘slim’. 

The purpose of this article is to create a factual and explicit comparison of the systems we have on show at Sky House and others on the market, to provide homeowners and local architects with an independent guide to help their selection and specification. 

Whether you’re an architect refining a glazing specification, a developer comparing performance against budget, or a homeowner trying to understand what you’re actually being quoted, this guide is designed to give you a clear, independent view of the leading slim sliding door systems on the market. 

How Have We Assessed These Slim Sliders?  

This article is only looking at slim framed external aluminium systems. We are not looking at steel and timber sliders and are only looking at external systems with with sightlines no larger than 26mm. Anything larger than 26mm would no longer be classed as ‘slim’.  

As all the slim sliders in this article are aluminium framed and have narrow sightlines and minimal framing, we are not comparing sightlines or materials too extensively. All sliders in this comparison have a vertical sightline (where the sliding panes meet) of between 20-26mm.  

Similarly, all these slim sliders have a flush threshold, so this is not part of the comparison.  

We have broken the comparison into the below sections. Feel free to click on these and jump to the place in the article you want to explore.  

Design & Aesthetics 

Configuration & Design Flexibility 

Security & Locking Systems 

Thermal Performance 

Thresholds & Accessibility 

Panel Sizes & Engineering Capability 

Weather & Acoustic Performance 

Glass & Finish Options 

Which system is right for your project? 

This means the comparison focuses on the areas that most directly affect how the doors look, perform and function on a real project. 

Re-Branded Names for Slim Sliding Door Systems  

This is particularly important when comparing quotes, as different suppliers may present the same system under different names, leading to misleading price or performance differences. 

It is common practice for some glazing companies to re-brand their slim sliding door systems in order to limit their competition. This is standard practice when a glazier; is not offering a unique system, they do not have exclusivity for that system or they know the system is offered by multiple other competitors.  

In order to keep this comparison simple, below is an overview of all of the minimally framed sliding door systems we are aware of and what the true product is. That way, you can ensure you are comparing costs and performance properly (rather than just comparing different costs for the same system!).  

Base System	Rebranded as...
Cortizo COR Vision	This is the most re-branded system we have come across. Below are just some of them we are aware of:   SL320 from ODC  PanoLUX from Cherwell  Origin Inifiglide from FinePoint
Cortizo COR Vision+	Heavily rebranded by multiple companies including:   SL700 from ODC  PanoLUX+ from Cherwell
Solarlux Cero III	SL800 from ODC
Ultraline	Sightline Aluminium Glazing  minima sliding
Sunflex SF60 and SF80	SF60 and SF80 from ID Systems
Orama Omicron	Infiniglide 6 from Finepoint

The below products do not allow their systems to be re-branded, therefore if you see someone selling these sliding doors, you know exactly what system that is.  

Sliding Door Range / System	Available from?
Keller minimal windows	Only available from IQ Glass in the UK, they have had exclusivity since 2011.
Sky-Frame	Various dealers in the UK including Crest Architectural Glazing, Alco Glass Systems, Cantifix and Clear Living.
panoramah!	Various dealers in the UK including HBD Systems, Camel Glass, John Knight and Fusion Glazing.

What systems are available to see at Sky House?  

At Sky House we have a large number of systems and manufacturers on show throughout the building. We have included all of these systems in our comparison. (Come and visit us to see any of these in person.)  

Keller minimal windows sliding door

Keller minimal windows 4+  

Keller minimal windows NGS  

panoramah ah!38 

Orama Omicron  

Sieger Slim Sliding Doors  

Sieger XL Sliding Doors  

What other systems are we also going to compare?  

In addition to the above, we are also going to compare the below systems as these are common systems our visitors mention when coming to us to explore slim framed sliding doors:  

Sky-Frame 2 and 3  

RCN EXP36 and EXP54 

Hyline HY40  

Cortizo COR vision 

Cortizo COR vision plus  

Solarlux Cero III 

Maxlight  

Ultraline 

Vitrocsa   

Sunflex SF60 and SF80  

What Have We Not Included?  

Before we start, we want to clarify by what we are classing a ‘slim sliding glass door’. 

There are many systems on the market that claim the title ‘slim’, however for us to consider a sliding door ‘slim’ we are looking for a slim vertical profile (no larger than 26mm) and minimal visible frame at the head, base and sides.  

For example, the Sunflex SVG20 (sold by ID Systems as the EDGE2.0) is often mentioned by our visitors as a patio door they are considering for their project however, the EDGE2.0 is not a true slim sliding door. Although the interlocks are narrow, the system has a large surrounding frame at the head, base and the outer edge of the sliding door aperture.  

Whilst this may be a cost-effective alternative for those looking for a patio door, the system is not a true ‘ultra-slim sliding door’ as ID Systems marketing suggests.  

Similarly, the SCG30 from Sunflex has a 30mm sightline so has not been included.  

We regularly see these systems mentioned by visitors when they first come to Sky House, so it is important to clarify how they differ from true slim sliding systems. 

The Comparison  

Design & Aesthetics Comparison  

The visual appeal and minimalism of these slim sliders is often the primary drive for most buyers. For homeowners and designers, this is often the most important factor, as it directly impacts how open, minimal and connected the space feels.  

For clarity, below are the definitions of what each bit of a frame is called:  

Interlock, the vertical sightline where two sliding panes (or a fixed and sliding pane) meet.  

Base frame, the visible frame above the finished floor level (FFL)  

Head frame, the visible frame below the interior / exterior ceiling finish  

Side frame, the visible frame at the side of the whole sliding door opening  

The most important measurements to create that true merging of internal and external spaces is the vertical sightline and the base frame.  

A small base frame means that there is no visible division between the internal and external floors, and the eye is drawn outwards.  

A narrow sightline makes the thermal barrier between inside and out nearly invisible, creating the indoor-outdoor aesthetic most common in modern living and architecture. 

Table: Which slim sliding doors look the most minimal? 

System	Interlock Size (mm)	Base Frame Visibility Above FFL (mm)
Keller minimal windows	21	~8
Keller minimal windows NGS	26	0 (fully concealed option)
panoramah ah!38	20	~8
Orama Omicron	~24+ (varies with height)	0
Orama Omega	~24+ (varies with height)	0
Sieger Slim	20	~6
Sky-Frame 2	20	~5
Sky-Frame 3	20	~5
RCN (EXP36 / EXP54)	21	~9
Hyline HY40	18	~18
Cortizo COR Vision	20	~6
Cortizo COR Vision Plus	25	~6
Solarlux Cero III	34	~34
Maxlight	20	~100+
Ultraline	20	~20
Vitrocsa	22	~18
Sunflex SF60	30	~37–55

While many systems achieve similar interlock sizes of around 20mm, the biggest visual difference often comes from how the base frame is installed. Fully concealed thresholds (0mm visible frame) deliver the cleanest architectural result, but may involve more complex installation. 

Ultra-minimal systems (best overall visual performance) 

Keller minimal windows 

NGS 

panoramah 

Sky-Frame 

Sieger Slim 

 Balanced minimal systems 

 Cortizo 

RCN 

Vitrocsa 

Orama 

 Less minimal / more visible frame  

Sunflex 

Ultraline

Maxlight 

Cero  

Configuration & Design Flexibility Comparison  

When comparing slim sliding door systems, configuration flexibility is where many products begin to separate. 

At a basic level, most systems allow sliding panels across multiple tracks with options for fixed panes, pocketing into walls, and standard corner openings. 

However, more advanced systems go much further, offering architectural freedom such as curved glazing, multi-axis openings, façade integration, and complex combinations of fixed and sliding elements. 

This is where architects and developers will see the biggest differences between systems, particularly on more complex or design-led projects. 

To make this easier to understand, the systems are grouped into: 

Basic systems which are suitable for most residential and straightforward architectural projects 

Advanced systems are designed for large-scale, complex, or highly bespoke architectural designs 

Basic Systems 

These systems offer the core configurations expected from a modern slim sliding door, including linear sliding, pocket doors, and standard corner openings. They are typically best suited to residential extensions, new builds, and projects where simplicity, cost control and reliability are priorities. 

Table: Comparison of Basic Systems 

System	Sliding Types	Tracks	Corner Options	Pocket Capability	Special Systems
Sieger Slim	Linear sliding, sliding + fixed	Up to 3 tracks (up to 6 sashes)	90° corner opening	Yes	—
Cortizo COR Vision	Sliding (multi-panel), fixed + sliding	1–3 tracks	90° corner (track-dependent)	Yes (minimum 2 tracks)	—
Cortizo COR Vision Plus	Sliding (multi-panel), fixed + sliding	1–4 tracks	90° corner (no mullion)	Yes (minimum 2 tracks)	—
Sunflex SF60	Sliding, fixed + sliding	2–3 tracks	Corner options available	Not clearly stated	—
Orama Omicron	Sliding, fixed + sliding	Up to 3 tracks	Corner opening	Yes	—
Orama Omega	Sliding, fixed + sliding	Up to 3 tracks	Corner opening	Yes	—
Maxlight	Sliding, bi-parting	Limited configurations	90° corner opening	Yes	—
Ultraline	Sliding (multi-panel), fixed + corner	1–4 tracks	Glass-to-glass corners	Yes	—

Summary of Basic Systems 

These systems typically provide: 

Straightforward linear sliding layouts 

Optional pocket sliding for full openings 

Standard 90° corner openings 

However, they are generally limited to: 

Rectilinear designs (no curves or complex geometry) 

Fewer track and stacking variations 

No integration into full façade systems 

Advanced Systems 

Advanced sliding door systems are designed as modular architectural systems, rather than just doors. They allow far greater design freedom, enabling large-scale glazing concepts and technically complex installations. 

These systems are typically used in: 

High-end residential architecture 

Landmark projects 

Large-span glazing 

Structural glass façades 

Table: Comparison of Advanced Systems 

System	Sliding Types	Tracks	Corner Options	Pocket Capability	Special Systems
Keller minimal windows	Linear, pocket, curved, vertical sliding	Multi-track	Any angle (65°–177°), opening or fixed frameless.	Yes	Curved sliding, vertical sliding, façade (Highline), integrated pivot, shaped sliders, inclined sliders, biparting
Keller NGS	Sliding + fixed combinations, automated sliding	Up to 5 tracks	Opening or fixed frameless	Yes	Highline façade integration, advanced automation  Curved sliding,  integrated pivot, shaped sliders, inclined sliders
panoramah ah!38	Sliding, fixed, pocket	Unlimited track configurations	90° / 270° corners	Yes	Curved layouts, inclined/sloped glazing, automation
Sky-Frame 2 / 3	Classic sliding, pivot, sloped systems	Multi-track	Corner options	Yes	Arc (curved), slope systems, pivot integration
Vitrocsa	Sliding, pocket, curved, inclined	Multi-track	Corner opening	Yes	Curved sliding, inclined glazing
RCN (EXP36 / EXP54)	Sliding, fixed + sliding, multi-panel stacking	1–4+ tracks	90° corner opening	Yes	Central/inverted openings
Hyline HY40	Sliding, motorised sliding	Multi-rail (mono–quad)	Corner opening	Yes	Motorisation systems
SolarluxCero III	Sliding, fixed + sliding	Multi-track	Corner opening	Yes	Motorisation and control integration

Summary of Advanced Systems 

These systems offer: 

Fully modular configuration design 

Greater variation in:  

Track numbers 

Panel stacking 

Opening directions 

Advanced options such as:  

Curved sliding doors 

Inclined or sloped glazing 

Façade integration (glass walls rather than doors) 

Automated movement systems 

Key Takeaway 

While many slim sliding doors appear similar visually, their configuration capability can be dramatically different. 

Basic systems provide reliable, clean design solutions for most residential projects 

Advanced systems act as architectural tools, capable of creating complex glazed structures that go far beyond standard sliding doors 

In practice, the right choice depends on the ambition of the design: 

For straightforward openings and value-led projects, basic systems are often sufficient 

For large-scale, bespoke, or design-led architecture, advanced systems offer significantly more flexibility 

Security & Locking Systems 

Security in slim sliding doors varies significantly, not just in certification (RC2, RC3, PAS24), but in how the doors physically lock. While many systems use multi-point locking, higher-end systems often use vertical rod systems engaging into the floor and ceiling, which provide a more robust structural lock. 

While many systems quote similar security ratings, the way the door actually locks — and how the user interacts with it — can vary significantly. These differences affect not just security, but also usability and visible design details. For homeowners, the way a system locks and operates day-to-day can be just as important as its certification rating. 

We have looked at:  

How the lock physically works  

Where it is located  

User experience + design implications  

Any hidden limitations 

Table: Comparison of Security & Locking of Slim Sliders 

System	Certification	Lock Type & Operation	Location & User Interaction	Important Notes / Limitations
Keller minimal windows	PAS24 / RC2	Vertical rod locking (shoot bolts engage into floor and ceiling) via handle or key	Handle or key integrated into 21mm interlock (standard or fully hidden) at any height on the sliding leaf	Highly engineered system, adjustable handle height, clean design integration. Electronic locking and key locking also possible.
Keller NGS	RC3 + PAS24	Same vertical rod locking system (top + bottom engagement)	Hidden or minimal handle or key, can fully disappear into wall on closing edge. Locking point at any height on the sliding door.	One of the most secure + discreet systems available Electronic locking and key locking also possible.
Cero III	RC2 / RC3	Rod-based locking system engaging vertically	Handle operated within profile	Strong mechanical locking aligned with system engineering
Sky-Frame 2 / 3	RC2 (upgradeable)	Multi-point locking integrated into vertical profile	Conventional handle operation within frame	Can upgrade security, but locking is side-based rather than vertical
Vitrocsa	RC2	Multi-point locking (various options including electric)	Typically side-profile handle or integrated controls	Flexible but less standardised approach
RCN	RC2	Interlock-based multi-point locking operated via sliding block	Small control block on interlock	Similar to panoramah; minimal but less tactile and less premium feel
panoramah ah!38	RC2	Multi-point mushroom locking operated by sliding plastic block	Plastic block located in interlock, manually slid up/down	Key limitation: plastic component, limited colour options (typically black), visible within minimal sightline which can affect design consistency
Hyline HY40	Not stated	Concealed locking system (unclear mechanism)	Appears hidden within wall/frame system	Lack of clear technical detail on operation or certification
Sieger Slim	PAS24	Multi-point mushroom locking activated by flipping integrated lever	Small lever on lead edge of sliding panel	Clean visually but conventional system logic
Cortizo Vision / Plus	PAS24 / RC2	Multi-point mushroom locking via lever	Lever integrated into lead panel	Typical system, reliable but not advanced
Sunflex SF60	RC2	Multi-point locking with mushroom bolts	Handle-operated within frame	Conventional engineered system
Ultraline	PAS24	Fully electronic head locking system	Operated via wall switch or keypad; no traditional handle	Major difference: no mechanical handle, reliance on electronics, manual override required via hidden access panel
Maxlight	Part Q / PAS24 (lock only)	Either base-mounted deadlock or 3-point side lock	Key-operated cylinder (side or base)	Lock is compliant, but full system not tested; more residential-grade solution
Orama Omicron / Omega	RC2	Locking system not clearly documented	Limited available detail	Lack of clarity on operation and user interface

Two systems with the same security rating can feel completely different in use. Systems with vertical locking rods engaging into the floor and ceiling generally provide a more robust and engineered solution, while interlock or side-based locking systems are simpler but often more visible and less refined in operation. 

Key takeaway: security  

Most secure systems: Keller NGS, Keller minimal windows, Cero 

Mid-tier security: Sky-Frame, Vitrocsa, panoramah 

Basic / conventional: Sieger Slim, Cortizo, Sunflex

Key takeaway: Usability & Design of Locks 

Best (fully integrated, minimal, intuitive): Keller minimal windows, Keller NGS, Cero III 

Good (clean but conventional systems): Sky-Frame, Vitrocsa, Sieger Slim, Cortizo systems, Sunflex SF60 

Compromised (visible or non-ideal design solutions): panoramah ah!38, RCN, Ultraline, Maxlight, Orama systems

Thermal Performance 

This is a key area for developers and architects working to meet Building Regulations and future energy standards. Thermal performance is heavily influenced by glazing thickness and frame design. While many systems quote strong Uw values, these are often dependent on specific glass build-ups. For most homeowners and many developers, this can be one of the hardest areas to interpret, as headline figures do not always reflect real-world performance. 

How to Interpret Thermal Performance 

When comparing slim sliding doors, thermal performance is often reduced to a single number, the Uw value. However, this figure on its own does not always give the full picture. 

The Uw value represents the overall heat loss through the combined frame and glass, but it is heavily influenced by glass specification, panel size and calculation method. This means two systems with similar quoted Uw values may perform very differently in real-world conditions. 

Your glazier will be able to give you an exact Uw value for your exact size, shape and configuration of doors quoted. You can then use this to ensure that the thermal performance of your intended door meets the thermal performance requirements of your project.  

Why does the thermal break location matter?  

On the table below you will see we have investigated where in the sliding door frame the thermal break is. You might wonder why. This is because, whilst all these systems are ‘thermally broken’ (meaning there is a strip of material that doesn’t conduct heat, normally a polyamide, in the frame, limiting heat energy movement through the metal frame) where the thermal break sits in the frame can limit its effectiveness.  

The most effective design for a thermal break is for the thermal break of the fixed frame and sliding sash to completely line up, creating a solid and continuous thermal break throughout the entire system. This should then line up with the insulating layer of gas within the glass unit.  

In practice, the most effective thermal break design is a continuous, aligned barrier that runs through the entire frame and sliding sash, and connects directly with the insulating gas layer of the glass. 

Systems that only include thermal breaks within the tracks or use segmented inserts allow heat to bypass the insulation layer more easily, resulting in weaker real-world performance compared to systems with true continuous thermal separation.

Table: Comparison of Thermal Performance of Slim Sliding Doors

System	Typical Uw Value	Thermal Break Type	Thermal Break Design & Alignment	Key Notes
Keller minimal windows	≥1.1 W/m²K	Fully continuous (optimal)	Continuous thermal break through frame and sash, aligned with insulating glass cavity	Consistent real-world performance
Keller NGS	From ~0.6 W/m²K	Fully continuous (deep, optimal)	Deep continuous thermal break through frame, sash and glass line (increased depth across NGS variants)	One of the most advanced thermal systems
Cero III	≤0.8 W/m²K	Fully continuous (optimal)	Continuous thermal separation aligned across full system depth and glazing line	High-performance engineered system
Ultraline	~1.17 → 0.73 W/m²K	Continuous (good)	Continuous thermal break through frame and sash, aligned reasonably well with glass	Strong for system type
panoramah ah!38	~1.16 W/m²K	Partially continuous	Thermal break within frame and profiles, but not fully aligned through system depth	Improved in triple-glazed variant
Sky-Frame 2 / 3	~1.15 → 0.66 W/m²K	Segmented	Thermal breaks between tracks and in frame sections, not fully continuous through sash–glass alignment	Good performance, not fully aligned
Vitrocsa	~0.97 W/m²K	Segmented	Thermal breaks in frame and sash, but discontinuous across full system line	Performance varies by configuration
RCN (EXP36 / EXP54)	~0.8 W/m²K	Segmented	Thermal breaks in sash and between tracks, deeper for triple systems but not fully continuous	Dependent on correct glass
Sieger Slim	~1.3 / ~0.9 W/m²K	Segmented	Thermal breaks within sash and fixed frame between tracks	Good mid-range performance
Cortizo COR Vision Plus	≥0.9 W/m²K	Segmented	Thermal breaks between tracks and within sash profiles	Limited by system depth
Cortizo COR Vision	≥1.3 W/m²K	Segmented	Shallow thermal breaks in frame and sash	Entry-level thermal performance
Sunflex SF60	~0.8 W/m²K (nominal)	Claimed continuous (limited)	Continuous break claimed, but shallow system limits alignment with glass cavity	Real-world performance limited
Orama Omicron	~1.2 W/m²K	Discontinuous	Small polyamide breaks in centre of tracks and at junctions only	Heat can bypass break easily
Orama Omega	~1.2 W/m²K	Discontinuous	Similar segmented breaks at track centres and junctions	Limited thermal efficiency
Hyline HY40	Not stated	Unknown	No clear published information on full thermal break alignment	Lack of transparency
Maxlight	Not stated	Basic segmented	Thermal breaks in frame and sash but with no detailed alignment info	No verified performance

While Uw values are often used as the headline comparison, the location and continuity of the thermal break is a better indicator of real thermal performance. Systems with continuous thermal separation through the full frame and glass line typically perform more consistently than those relying on segmented or track-only thermal breaks. 

Key takeaway 

Best thermal: Keller NGS, Sky-Frame 3, Cero, RCN 

Balanced: Vitrocsa, panoramah, Sieger XL 

Lower performance: Cortizo Vision, Maxlight  

Thresholds & Accessibility 

For homeowners and end users, this has a direct impact on day-to-day usability, maintenance and long-term performance.  

Threshold design plays a major role in both the appearance and everyday usability of a slim sliding door system. While many products can achieve a flush internal floor level, the way the threshold is detailed below the surface can vary significantly. 

At a basic level, most systems offer a standard flush threshold suitable for residential use. However, more advanced systems provide fully concealed or “invisible” base details, alongside accessible, barrier-free options designed for seamless indoor–outdoor transitions. 

The key differences come down to how each system balances aesthetics, drainage, accessibility and long-term practicality, particularly in climates where weather performance and maintenance need to be carefully considered. 

Beware the ‘Invisible’ Threshold  

This is one of the most common questions we are asked by visitors at Sky House, particularly on contemporary residential projects.  

While many systems promote an “invisible threshold” as the ultimate minimal design feature, it’s important to approach this option with caution, particularly for UK projects. 

Visually, the concept is appealing. The entire base frame is concealed below the finished floor level, creating a seamless transition between inside and out. However, this comes with trade-offs that are not always clearly explained. 

By burying the sliding mechanism below the floor, the system becomes far less accessible. This can lead to practical issues over time, especially in external environments. For example, debris such as stones or dirt can enter the track, and in some cases the finished floor has had to be removed to access and resolve relatively minor issues. 

There are also performance considerations. Fully recessed systems can, in some cases, compromise drainage, air tightness and thermal performance compared to more accessible threshold designs. 

For this reason, while invisible thresholds can work well in certain controlled environments, they are not always the most robust or practical solution for everyday use in the UK climate. You can always visit Sky House and speak to one of our team if you are unsure or want some advice.  

Table: Comparison of Threshold Systems

System	Flush Threshold	Invisible Threshold	Accessibility Notes
Keller minimal windows	Yes	No	Tested to DIN 18040-1, DIN 18040-2 showcasing strong barrier-free compliance
Keller NGS	Yes	Yes (the Floor base option is invisible AND still accessible so removes the maintenance issues of the invisible threshold)	Tested to DIN 18040-1, DIN 18040-2 showcasing strong barrier-free compliance. Best balanced invisible solution
panoramah	Yes	Yes
Sky-Frame	Yes	Yes
Vitrocsa	Yes	Yes
RCN	Yes	Yes
Cero III	Yes	No	Visible but engineered
Sieger Slim	Yes	No
Cortizo Vision	Yes	Limited
Sunflex SF60	Yes	Raised option	Visible frame often higher
Ultraline	Yes	No
Hyline	Yes	Yes
Maxlight	Yes	No
Orama systems	Yes	Yes

Key takeaway 

Best invisible thresholds: Keller NGS, Vitrocsa, panoramah, Sky-Frame 

Best practical UK solution: Keller standard system 

Simplest solutions: Sieger Slim, Cortizo 

Panel Sizes & Engineering Capability 

Panel size is one of the clearest indicators of how engineered a sliding door system really is. While many products appear similar visually, their ability to support large, heavy glass panels varies significantly. For architects designing large openings, this often determines what is physically achievable within the project. 

At a basic level, most systems can handle standard residential panel sizes, typically up to around 3–4 metres in width or height. However, higher-end systems are designed to support much larger panels, enabling full-height glazing, wider openings and fewer visible divisions. 

The key differences come down to weight capacity, structural design and how well the system distributes load, which ultimately determines whether a system can achieve true large-format glazing or remains limited to more conventional sizes. 

Table: Comparison of Panel Capability

System	Max Panel Weight	Max Size	Notable Capability
Keller minimal windows	~500kg	Tested to 8.5m² per sliding panel and 4m tall, but evidence of significantly larger installations depending on project engineering	Highly adaptable
Keller NGS	1500kg	Up to 6m+ tall / up to 18m² per panel	Market-leading
panoramah ah!38	1000kg	Max leaf height 6m, max leaf width 6m, max area 19m² (double glazing) or 6m² (triple glazing)	Strong flexibility
Orama Omicron	1000kg	Max sliding leaf area 12m², max fixed leaf area 19.5m², panel height dependent on specification	Balanced system capability
Orama Omega	1000kg	Max sliding leaf area 12m², max fixed leaf area 19.5m², panel height dependent on specification	Strong acoustic + thermal variant
Sky-Frame 2 / 3	Not explicitly stated	Typical tested size ~2.3m × 4m, larger available on request depending on project engineering	Design-led system
Vitrocsa	Not explicitly stated	Max panel area ~18m²+, size dependent on configuration and engineering	Proven large-format system
RCN (EXP36 / EXP54)	Not explicitly stated	EXP36: up to 5m tall / 12m² per panel; EXP54: up to 6m tall / 18m² per panel	High-performance large panels
Solarlux Cero III	1000kg	Panels up to ~4m × 6m, large-format glazing depending on configuration	Structural system
Hyline HY40	Not explicitly stated	Panel size up to ~18m², height up to 6m (subject to engineering)	Large panels with ultra-slim sightline
Sunflex SF60	~800kg	Panel sizes dependent on configuration, typically mid-to-large format sliding panels	Balanced engineering system
Cortizo COR Vision Plus	700kg	Max panel size approx. 4m × 4m	Larger panels in mid-tier range
Sieger Slim (XL)	400kg manual / 700kg motorised	Up to 4m width × 4m height, max ~14m²	Strong for mid-tier system
Cortizo COR Vision	~320kg	Max panel size approx. 2.5m width × 3.0m height	Smaller-format system
Ultraline	225–340kg	Max panel area ~9m² (double) / ~5.4m² (triple)	Limited structural capability
Maxlight	Not stated	No confirmed panel size or weight data provided	Limited technical transparency

While several systems claim large panel sizes, the key difference is whether those sizes are fully tested, routinely achievable, or dependent on project-specific engineering. 

Key takeaway 

Top engineering systems: Keller minimal windows and NGS, Cero, RCN, panoramah 

Mid-tier: Sieger Slim, Sunflex, Cortizo Plus 

Limited systems: Ultraline, Cortizo Vision 

Weather & Acoustic Performance 

Weather performance is one of the most important but often overlooked factors when comparing slim sliding door systems. While many products achieve similar air tightness ratings, the real differences begin to appear when looking at water resistance and wind performance. 

At a basic level, most modern systems reach high standards for air permeability and are suitable for high performance residential builds. However, performance under driving rain and high wind loads can vary significantly depending on how the system is engineered and installed. This is particularly relevant for exposed sites or urban locations where performance consistency is critical. 

Acoustic performance also plays a growing role, particularly in urban environments, where thicker glass and better sealing can noticeably reduce external noise. Higher-end systems typically combine stronger weather resistance with improved acoustic insulation, while more simplified systems may offer solid performance but with greater variation depending on configuration. 

 Table: Comparison of Weather Performance

System	Air	Water	Wind	Acoustic
Keller minimal windows	Class 4	7A–8A+	C4–C5	39–43 dB
Keller NGS	Class 4	8A+	C5	~44 dB
panoramah	Class 4	E900	C5	~41 dB
Sky-Frame 3	Class 4	E900	C5	~44 dB
RCN	Class 4	E1200+	C5	41–44 dB
Cero III	Class 4	E750	C5	~44 dB
Sieger Slim	Class 4	7A	C5	~41 dB
Cortizo Vision	Class 4	7A	C5	~41 dB
Cortizo Vision Plus	Class 4	7A–9A	C3–C4	~43 dB
Sunflex SF60	Class 4	9A	C3	—
Ultraline	Class 4	9A	C3	35–41 dB
Vitrocsa	Class 3–4	7A–9A	C3–B5	~36 dB

Key takeaway 

Best performance: Keller NGS, RCN, panoramah 

Strong mid-range: Sieger Slim, Cortizo 

More variable: Vitrocsa, Sunflex

Glass & Finish Options 

Glass specification and frame finishes play a key role in both the performance and appearance of a slim sliding door, but they are often less straightforward to compare than headline figures like sightlines or Uw values.  

While most systems offer a similar palette of powder-coated and anodised finishes, the real differences lie in glass thickness, the ability to accommodate high-performance triple glazing, and how the glass integrates with the frame. Higher-end systems tend to support significantly thicker glass units, enabling improved thermal performance, larger panel sizes and better acoustic control, whereas more entry-level systems are often limited to thinner double-glazed units and more standardised finish options. 

This becomes increasingly important on larger, higher-performance projects where glass specification directly affects both performance and design. 

Why is the maximum glass thickness important?  

This might seem like a strange thing to compare. Why do I care how thick my glass unit is? However, if you want higher performance, taller sliding doors or more complex glass designs, you need a thicker glass unit. If your sliding door frame cannot hold that glass thickness you will need to make compromises on the design or performance.  

Additional layers into a glass unit increase the thickness. I am not just talking about double or triple glazing, I am also talking about laminates. Laminates can be added into a glass specification to increase security, acoustic performance or change the visual appearance of the glass.  

Taller doors or areas of higher wind load will need a thicker glass unit to allow for a larger gas cavity which acts as a deflection zone for the external glass to flex and move naturally without damaging the glass unit.  

It is also really useful to understand max glass thickness in order to professionally assess the validity of some supplier’s thermal performance claims.  

For example, the RCN EXP36 sliding door has a maximum glass thickness of 36mm, so can only really take a double-glazed unit. In the RCN thermal performance information, they say they can achieve a Uw value of 1.1 W/m2K stipulating that this thermal performance is only possible with a glass unit with Ug value of 0.7 W/m2K. But a Ug value of 0.7 W/m2K is not possible from a double-glazed unit. So this thermal performance will never be actually possible in real life.  

So whilst max glass thickness is less important for a standard rear patio door slider, if you are looking for a larger sliding door or better performance then it is something you should take a look at.  

Table: Comparison of Glass & Finishes

System	Max Glass Thickness	Glazing Unit	Frame Finishes
Keller minimal windows	26–32mm	Double/triple	Wide range of options (PPC full RAL range, anodised or special)
Keller NGS	Up to 74mm	Triple	Wide range of options (PPC full RAL range, anodised or special)
panoramah	~38mm	Double/triple	Wide range of options (PPC full RAL range, anodised or special)
Sky-Frame	30–54mm	Double/triple	Wide range of options (PPC full RAL range, anodised or special)
Vitrocsa	32–44mm	Double/triple	Wide options
RCN	EXP36 = 36mm, EXP54 = 54mm	Double/triple	Anodised or powder coated
Cero III	48–54mm	Triple	Premium finishes
Sieger Slim	26–54mm	Double/triple	Good range (RAL, anodised)
Cortizo Vision	~30mm	Double	Standard / limited
Cortizo Vision Plus	~56mm	Triple	Standard / limited
Sunflex SF60	~32mm	Double	Standard / limited
Ultraline	24–46mm	Double/triple	Limited palette
Hyline	~38mm	Triple	Standard / limited
Maxlight	No info	Double only	Standard / limited

Key takeaway 

Most flexible: Keller NGS, Cero, RCN 

Balanced: Sieger Slim, Cortizo Plus 

Limited: Maxlight, basic Cortizo 

Which system is right for your project? 

Choosing the right slim sliding door system is less about identifying a single “best” product, and more about understanding which system aligns with the design intent, performance requirements and priorities of your project. 

At Sky House, we see a wide range of projects, from design-led residential extensions through to highly engineered, large-scale homes. In many cases, homeowners, architects and developers are working together, so the right system is usually the one that balances aesthetic ambition, technical performance and practical considerations. 

Below is a guide to how different systems tend to align with different project priorities. 

For projects focused on architectural impact and large-scale glazing 

For projects where glazing is a defining architectural feature, the capability of the system becomes critical. This typically includes large openings, minimal framing, complex geometry or bespoke detailing. 

Systems such as: 

Keller minimal windows 

Keller NGS 

Cero 

panoramah 

Sky-Frame 

are commonly specified on projects where the glazing is integral to the architectural concept. These systems offer advanced engineering capability, larger panel sizes and a high degree of design flexibility, making them particularly well suited to ambitious, design-led homes. 

Alongside this architectural freedom, they are also designed to meet the more demanding side of modern building design. These systems are extensively tested and certified, with performance levels that go beyond standard regulatory requirements in areas such as thermal efficiency, weather resistance and structural capability. 

This allows architects and clients to push the visual boundaries of a project without compromising on how the building performs in practice. The result is glazing that not only delivers a refined, minimal aesthetic, but also supports the long-term comfort, efficiency and durability expected of contemporary homes. 

For projects where budget and usability are key priorities 

In some projects, the focus is on creating a clean, contemporary aesthetic with straightforward operation and reliable performance, rather than pushing the limits of engineering capability.  

Systems such as: 

Sieger Slim 

Cortizo COR Vision 

Hyline 

Sunflex SF60 

are often selected where the design intent is centred around simplicity, everyday usability and consistent delivery, particularly in more typical residential layouts where budgets are more constrained.  

For projects requiring maximum flexibility in design approach 

Some systems stand out not just for performance, but for the level of design freedom they enable. This can include curved glazing, complex opening configurations, or integration into wider façade systems. 

Systems such as: 

panoramah 

Vitrocsa 

Sky-Frame 

Keller systems 

are often considered when flexibility is a key requirement, allowing architects to explore more complex or unconventional designs. 

Many slim sliding door systems appear very similar on paper, but the differences in operation, detailing, engineering and finish become much clearer when experienced in person. 

At Sky House Design Centre, you can view multiple systems side by side, compare how they feel and function, and discuss your project directly with specialists across different manufacturers. 

If you are at the stage of comparing options, visiting in person is often the most effective way to understand which system is right for you. 

See These Systems Side by Side at Sky House 

One of the biggest challenges when comparing slim sliding doors is that most suppliers only show one system in isolation. 

At Sky House Design Centre, you can view multiple systems side by side, understand the real differences in operation and detailing, and speak directly with specialists across different manufacturers. 

If you are planning a project and want to compare options in person, book a visit or get in touch with the team.