Aluminium has changed what is possible in window design. Its strength supports slimmer frames and larger panes, whilst modern thermal breaks and advanced glazing provide far better insulation than older systems.
However, individual systems prioritise different features – from passive-house performance and outward opening to concealed sashes and traditional steel-look design. The lowest Uw value will not always indicate the best choice, as appearance, available configurations, weather resistance and price must also suit the project.
In this guide, we compare seven systems from well-known brands available in the Fenbro range: Aluprof, Reynaers and Aliplast. We will explore their main differences, advantages and limitations to help you make an informed decision.
Which aluminium window systems are included in this comparison?
To show how varied aluminium windows can be, we picked products that represent different levels of thermal performance, opening methods and architectural styles:
- MB-79N SI from Aluprof
- MB-86N SI from Aluprof
- MB-104 Passive SI from Aluprof
- MB-79N Casement from Aluprof
- MaxLight Modern from Aliplast
- SlimLine 38 from Reynaers
- MB-86 US from Aluprof
Aluminium window system comparison
Here’s an interesting fact: all seven systems in this comparison have three chambers. What sets them apart is the design of the thermal break, the use of additional insulating inserts, the sealing system, glazing specification and complete window configuration. Below, you can read about each product in more detail.
Aluprof MB-79N SI – our absolute bestseller
We’d like to begin with MB-79N SI by Aluprof, one of Fenbro’s bestselling aluminium systems. It has been designed as a flexible solution for residential and commercial projects, offering strong technical performance without limiting buyers to one particular architectural style or window configuration.
The system has a frame depth of 70 mm and a window sash depth of 79 mm. Its three-chamber profiles incorporate a thermal break, additional insulating inserts and a specially shaped two-component central gasket. Depending on the complete configuration, U-value can range from 0.64 to 0.83 W/m²K here. Also, glazing units up to 63 mm thick can be used, leaving plenty of room for advanced triple-glazed packages.
MB-79N SI performs very well when exposed to changing weather conditions. It achieves Class 4 air permeability, E1950 water resistance and C5 wind resistance. The maximum stated dimensions of a tilt-and-turn sash reach 2,700 mm in height and 1,700 mm in width, although the final permitted size always depends on the glazing, hardware and structural requirements of the individual project.
Another important advantage is versatility. MB-79N SI can be used to create fixed, side-hung, tilt, tilt-and-turn and tilt-and-slide windows, as well as external doors and larger glazed structures.
Best suited to: customers looking for a versatile aluminium system that connects strong thermal and weather performance with extensive configuration possibilities.
Consider another system if: Passive House certification, outward opening, a concealed sash or a strongly defined steel-look design is one of the main project requirements.
Aluprof MB-86N SI – strength for larger and heavier structures
Second one on the list is MB-86N SI by Aluprof – aimed at energy-efficient projects that require robust aluminium profiles and greater glazing capacity.
The system has a frame depth of 77 mm and a three-chamber construction with a thermal break. A multi-component central gasket helps insulate the space between the sash and frame, while glazing units up to 67.5 mm thick can be accommodated. The maximum stated sash dimensions are 1,700 × 2,400 mm, with a maximum weight of 150 kg. This makes MB-86N SI suitable for large and relatively heavy window structures, subject to the final design and structural calculations. Not to mention an outstanding U-value of 0.76 W/m²K and acoustic insulation of 29–38 dB. The system also achieves Class 4 air permeability, E1500 water resistance and C5 wind resistance.
Best suited to: energy-efficient projects requiring strong profiles, thicker glazing units or large and heavy window structures.
Consider another system if: the lowest available U-value, outward opening or concealed-sash aesthetics is the main priority.
Aluprof MB-104 Passive SI – built for passive construction
MB-104 Passive SI by Aluprof is the most thermally advanced Aluprof system in this comparison. It has been developed specifically for energy-efficient and passive buildings, and its performance has been confirmed by certification from the Passive House Institute Darmstadt.
Its frame has an installation depth of 95 mm, while the sash depth reaches 104 mm. This makes it the deepest system in the Aluprof group included here. It can accommodate glazing units up to 72 mm in the frame and 81 mm in the sash – the greatest glazing capacity among all seven systems. The manufacturer reports a U-value ranging from 0.53 to 0.68 W/m²K – the best thermal performance in the comparison!
MB-104 Passive SI achieves Class 4 air permeability, AE1800 water resistance and C5/B5 wind resistance. Its stated acoustic insulation is 29–38 dB. Maximum sash dimensions reach 1,700 × 2,900 mm, although the sash weight is limited to 106 kg and every large configuration must be assessed individually.
The deeper construction and extensive insulation make MB-104 Passive SI a highly specialised option. For a standard renovation without demanding energy targets, its capabilities may go beyond what the project actually requires. A shallower and less specialised system may then provide a more appropriate balance.
Best suited to: passive houses, highly energy-efficient new builds and projects where reducing heat loss is the overriding priority.
Consider another system if: a shallower frame, outward opening, concealed-sash design or steel-look appearance is more important than Passive House-level performance.
Aluprof MB-79N Casement – designed for outward opening
Next we have Aluprof MB-79N Casement that stands apart from the previous systems because it opens outwards.
The product specification lists a frame depth of 70 mm, while the structural depth of the window profiles is 79 mm. Its three-chamber construction includes a 34 mm insulation chamber positioned between the thermal breaks. A specially shaped two-component central gasket supports thermal performance as well as water and air tightness. Glazing ranges from 14.5 to 53.5 mm in the frame and from 23.5 to 62 mm in the opening casement.
The producer lists a U-value of 0,91 W/m²K, acoustic insulation of 29–38 dB, Class 3 air permeability, 5A water resistance and C4 wind resistance. These figures are more modest than those offered by the strongest inward-opening systems in the comparison. If a project must meet a specific thermal requirement, the final window configuration should therefore be checked carefully.
The use of standard Euro grooves allows the installation of a wide range of fittings for outward-opening windows. Customers can also choose between concealed knife hinges and traditional visible hinges..
Best suited to: Irish and British building projects requiring top-hung or side-hung aluminium windows that open outwards.
Consider another system if: the lowest possible U-value, Class 4 air permeability, the highest weather resistance or an inward-opening tilt-and-turn configuration is required.
Aliplast MaxLight Modern – slender profiles with an industrial character
MaxLight Modern by Aliplast places greater emphasis on appearance. With the help of narrow aluminium profiles, it reduces the visual frame, thus maximising the glazing area and providing a modern look to the building envelope. The distinctive profile shape also introduces a subtle industrial character inspired by traditional steel windows.
The system has a frame depth of 75 mm and a sash depth of 84 mm. Its minimum combined frame-and-sash sightline is 70 mm, while glazing units up to 68 mm thick can be installed. This is the second-greatest glazing capacity in the comparison, exceeded only by MB-104 Passive SI. MaxLight Modern can be used to create fixed windows as well as inward-opening, single- or double-sash configurations with a tilt function.
Its estimated U-value is around 1.0 W/m²K. The system achieves Class 4 air permeability, E1650 water resistance and C5 wind resistance, giving it a strong set of weather-performance figures. This product from Aliplast meets the requirements of the RC2 burglary-resistance class.
It is also worth distinguishing this system from SlimLine 38 (described below): both are inspired by steel profiles, but MaxLight Modern offers a cleaner contemporary interpretation and SlimLine 38 provides more stylistic variants.
Best suited to: contemporary homes and design-led projects requiring slender profiles, large glazing areas and a subtle industrial influence.
Consider another system if: Passive House performance, outward opening, a concealed sash or a published high acoustic-insulation value is required.
Reynaers SlimLine 38 – perfect for steel-look lovers
Another product – SlimLine 38 from Reynaers – represents the most aesthetically striking window among the ones analysed in this article. It replicates the proportions of classic steel windows, but at the same time offers the strength, thermal insulation properties, and low-maintenance features that are typical of aluminium windows. Thus, this kind of window is great for modern architecture and replacement of old steel windows.
The system is available in three aesthetic variants. Classic uses sloped surfaces, Cubic introduces stepped detailing, and Ferro is characterised by sharp lines and shadow gaps. Different frame and sash styles can be mixed, providing considerably more design freedom than a single standard profile shape. Concealed hinges, hidden drainage and glass-corner solutions are also available.
SlimLine 38 has a frame depth of 99 mm and a sash depth of 86 mm. Despite having the deepest frame in the comparison, its visible profiles remain slender – installation depth and visible sightline are not the same measurement. The system accommodates double or triple glazing up to 55 mm thick. Maximum sash dimensions reach 1,200 × 2,800 mm, with a maximum weight of 170 kg.
In its best configuration, SlimLine 38 can achieve a U-value of 0.96 W/m²K and acoustic insulation of 44–46 dB. This profile also achieves Class 4 air permeability, 9A water resistance and C4 wind resistance.
Best suited to: renovations involving original steel windows, character properties and modern projects requiring narrow, highly distinctive aluminium profiles.
Consider another system if: the lowest U-value, the greatest glazing capacity, outward opening or Passive House certification is more important than steel-look aesthetics.
Interested in this type of design? Don’t forget to check the guide to slim-look windows.
Aluprof MB-86 US – minimalist look with a concealed sash
Finally, we have MB-86 US by Aluprof, a system developed for projects where the appearance of the window is just as important as its technical performance. Its defining feature is the concealed sash: when viewed from outside, the opening part is hidden behind the frame.
The system has a frame depth of 77 mm and a three-chamber construction with a thermal break. It can accommodate glazing up to 58.5 mm in the frame and 67.5 mm in the sash. Maximum sash dimensions reach 1,700 × 2,400 mm, with a maximum weight of 150 kg, allowing the profiles to support relatively large and heavy structures.
According to the manufacturer’s specification, MB-86 US has a U-value of 0.96 W/m²K and acoustic insulation of 29–38 dB. It also achieves Class 4 air permeability, E1500 water resistance and C5 wind resistance. These figures are identical to those listed for MB-86N SI, meaning that the choice between them is driven primarily by the desired appearance rather than a difference in headline performance.
The concealed sash gives MB-86 US a clear advantage over conventional visible-sash systems, but it does not provide the heritage-inspired detailing of SlimLine 38 or the stronger thermal performance of MB-104 Passive SI.
Best suited to: modern homes and minimalist façades where opening and fixed windows should have a consistent appearance
Consider another system if: concealed-sash design is not important or the project requires outward opening
Best aluminium window systems comparison: summary table
Too much information in the sections above? Don’t worry – we’ve brought the key specifications together in the tables below.
| System | Brand | Frame depth | U-value | Max. glazing thickness | Opening direction | Acoustic insulation | Price from* |
|---|---|---|---|---|---|---|---|
| MB-79N SI | Aluprof | 70 mm | 0.64–0.83 W/m²K | 63 mm | Inwards | Not specified | €309 net |
| MB-86N SI | Aluprof | 77 mm | 0.96 W/m²K | 67.5 mm | Inwards | 29–38 dB | €356 net |
| MB-104 Passive SI | Aluprof | 95 mm | 0.53–0.68 W/m²K | 81 mm | Inwards | 29–38 dB | €397 net |
| MB-79N Casement | Aluprof | 70 mm | 0.91 W/m²K | 62 mm | Outwards | 29–38 dB | €340 net |
| MaxLight Modern | Aliplast | 75 mm | 1.0 W/m²K | 68 mm | Inwards | Not specified | €316 net |
| SlimLine 38 | Reynaers | 99 mm | 0.96 W/m²K | 55 mm | Inwards | 44–46 dB | €435 net |
| MB-86 US | Aluprof | 77 mm | 0.96 W/m²K | 67.5 mm | Inwards | 29–38 dB | €362 net |
*Please note: all example prices apply to a 1000 × 1000 mm white fixed aluminium window with triple glazing.
The next table focuses on information about sealing, security and resistance to weather conditions:
| System | Gaskets | Air permeability | Wind resistance | Water resistance | Security level |
|---|---|---|---|---|---|
| Aluprof MB-79N SI | 2 | Class 4 | C5 | E1950 | Up to RC3 |
| Aluprof MB-86N SI | 2 | Class 4 | C5 | E1500 | Up to RC4 |
| Aluprof MB-104 Passive SI | 2 | Class 4 | C5/B5 | AE1800 | Up to RC3 |
| Aluprof MB-79N Casement | 3 | Class 3 | C4 | 5A | Not specified |
| Aliplast MaxLight Modern | 2 | Class 4 | C5 | E1650 | RC2 |
| Reynaers SlimLine 38 | 3 | Class 4 | C4 | 9A | RC2 |
| Aluprof MB-86 US | 2 | Class 4 | C5 | E1500 | Up to RC3 |
Quick picks: which aluminium window system should you choose?
The tables make the numerical differences easier to see, but the final decision will usually come down to one or two priorities that matter the most. Based on the published specifications, product features, reference prices and the experience of Fenbro Experts, here are our quick top picks:
- Best for thermal performance: MB-104 Passive SI
- Best for passive-house projects: MB-104 Passive SI
- Best balance of performance and price: MB-79N SI
- Best for outward-opening windows: MB-79N Casement
- Best for steel-look: SlimLine 38
- Best for minimalist concealed-sash design: MB-86 US
- Best industrial design: MaxLight Modern
Keep in mind – these recommendations should be treated as a starting point rather than a final decision. Talk to our Sales Specialists to figure out together which solutions would work best.
Top 3 bestselling aluminium window systems at Fenbro
The most popular aluminium window systems among Fenbro customers are Aluprof MB-79N, Aluprof MB-86 and Aliplast MaxLight Modern. Over the past 20 months, we have sold a total of 711 units across these three bestselling systems. Aluprof MB-79N accounted for 64.84% of these sales, MB-86 for 23.63% and Aliplast MaxLight Modern for 11.53%.
Conclusion – which aluminium window system is the best?
Congratulations, you’ve made it to the end of our article! If there is one thought to take away, it is this: the best system is not defined by a single parameter, but by how well its complete configuration matches your project’s technical requirements, preferred opening method, design, location and budget.
Would you like help narrowing down your options? Send us your requirements through our contact form, and our Specialists will prepare a personalised quote within two working days – completely free of charge!
Frequently Asked Questions
Where can I buy the best aluminium windows?
Fenbro is one of the best choices for customers looking for high-quality aluminium windows from leading European manufacturers, including Aluprof, Aliplast and Reynaers. Our Specialists can help you compare the available systems, select the right configuration and prepare a personalised quote for your project.
Which aluminium windows are the best?
There is no universal system for every project. The right choice depends on the required U-value, opening direction, window dimensions, architectural style, exposure to weather and available budget.
Which aluminium window system has the lowest U-value?
In the Fenbro range, MB-104 Passive SI by Aluprof has the lowest U-value, ranging from 0.53 to 0.68 W/m²K. Remember that the final result depends on the window dimensions, glazing and complete configuration.
Which aluminium windows offered by Fenbro open outwards?
MB-79N Casement by Aluprof is the outward-opening system in this comparison. It is available in top-hung and side-hung configurations commonly used in Irish and British properties.
Which aluminium window system in Fenbro’s range offers the best acoustic insulation?
SlimLine 38 by Reynaers has the highest estimated acoustic range in this comparison at 44-46 dB. Actual sound reduction will depend on the glazing package, window dimensions and installation.
What is the difference between MB-79N SI and MB-86N SI aluminium window systems?
MB-79N SI has a shallower 70 mm frame, a published U-value of 0.64–0.83 W/m²K and glazing capacity up to 63 mm. MB-86N SI has a 77 mm frame, accommodates glazing up to 67.5 mm and supports sashes weighing up to 150 kg, making structural strength one of its main advantages.
What is the difference between MB-79N SI and MB-79N Casement aluminium window systems?
Both Aluprof systems differ in their opening direction: MB-79N SI opens inwards, while MB-79N Casement opens outwards in top-hung or side-hung configurations. The SI version also offers a lower published U-value (0.64 – 0.83).
What is the difference between MB-86N SI and MB-86 US aluminium window systems?
Both systems share the same main performance figures in this comparison, including a U-value of 0.96 W/m²K, glazing up to 67.5 mm and Class 4 air permeability. The main difference is appearance: MB-86 US conceals the opening sash behind the frame when looked at from outside.
Which aluminium window system should I choose for a steel-look?
SlimLine 38 is the strongest choice for a distinctive steel-look appearance. It is available in three variants: Classic, Cubic and Ferro – you can choose which one suits your vision the most. Plus, Aliplast’s product, MaxLight Modern, offers a smoother and more contemporary industrial interpretation.
