Two frame materials cover the vast majority of replacement and new-build windows in the UK: aluminium and uPVC. Both are excellent, both are low-maintenance, and both can hit the security and thermal standards Building Regs demand. The right answer depends on the job — the budget, the look, the size of the openings and what the customer cares about most. Here's how they stack up.
The short answer
Choose uPVC when budget is the priority and the openings are a standard size — it's the cost-effective, well-insulated everyday choice. Choose aluminium when you want slim sightlines, large spans, a specific RAL colour or a premium finish that will still look sharp in 30 years.
Sightlines and looks
Aluminium is a structural metal, so it does more with less. Frames and sashes are slimmer, which means more glass and a cleaner, more contemporary look — a big reason it dominates on new-build, extensions and feature windows. It also holds crisp, square lines that suit modern architecture and, in a heritage profile, replicates old steel windows convincingly.
uPVC frames are bulkier because the plastic needs more material (and often internal steel reinforcement) to stay rigid. That's rarely a problem on a typical domestic casement, and modern flush-sash uPVC looks far better than the chunky profiles of twenty years ago — but if the customer wants maximum glass and minimal frame, aluminium wins.
Thermal performance
uPVC is naturally a good insulator, so it reaches low U-values easily and cheaply. Aluminium conducts heat, so it relies on a polyamide thermal break — an insulating barrier between the inside and outside of the frame — to perform. Modern thermally broken aluminium systems close the gap almost completely, and both materials comfortably meet the Approved Document L requirement for replacement windows (a Window Energy Rating of band B or better, or a U-value of 1.4 W/m²K or lower).
In practice: for the very best thermal number at the lowest cost, uPVC has a slight edge. For a demanding spec on aluminium, specify a triple-glazed, fully thermally broken system and the difference becomes marginal.
Cost
This is usually the deciding factor. uPVC is significantly cheaper — often around half the price of an equivalent aluminium window — which is why it remains the volume choice for replacement work and budget-led projects. Aluminium carries a premium for the material, the powder-coat finish and the slimmer engineering. On a whole-house replacement that gap adds up, so it pays to be clear with the customer about where the money goes.
Colour and finish
| Aluminium | uPVC | |
|---|---|---|
| Colour range | Virtually any RAL colour | White plus a growing range of foils/woodgrains |
| Dual colour | Yes — different inside and out | Available on many systems |
| Finish durability | Powder coat — very hard-wearing | Foil can fade or lift over decades |
| Feel | Premium, architectural | Practical, domestic |
If a customer has a specific colour in mind — a heritage green, an anthracite grey to match the doors, a bold RAL — aluminium gives you the freedom to match it exactly and know the finish will last.
Size, strength and large openings
Because aluminium is stronger, it spans further without deflecting. That makes it the natural choice for large feature windows, floor-to-ceiling glazing and anything structural. Push uPVC too far and you need heavier reinforcement and more frame — at which point aluminium often makes more sense anyway.
Lifespan and maintenance
Both are low-maintenance — a wipe-down is all either needs. The difference is longevity. A quality powder-coated aluminium window will typically last 40 years or more with the finish intact. uPVC has a shorter practical lifespan (commonly 25–35 years) and white frames can yellow slightly over decades of UV exposure. For a customer who wants "fit it and forget it for the long haul," aluminium justifies its premium.
Security and sustainability
Both materials achieve PAS 24 enhanced security and can be specified to Secured by Design — the frame material is far less important here than the locking, hinges and glazing. On sustainability, aluminium is infinitely recyclable without losing quality, while uPVC is recyclable but with a less circular end-of-life. Both are strong choices; aluminium tends to appeal to the more environmentally-led specifier.
How to steer the conversation
- Budget-led replacement, standard sizes: uPVC.
- Slim sightlines, large glass, modern look: aluminium.
- Specific colour that has to last: aluminium.
- Big spans or feature windows: aluminium.
- Best thermal value for money: uPVC.
- Mixed job? There's nothing wrong with uPVC on the rear elevation and aluminium on the front — spec each opening on its merits.
Whichever way the job goes, you don't need two suppliers for it. We carry the major aluminium and uPVC systems side by side, so a mixed-material project still comes back as one quote and ships on one delivery.
