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This is the question we are asked more than any other, and the honest answer is that both materials are good. They fail in different places and cost different amounts, and the right choice depends on the opening, the property and the budget rather than on which one is objectively superior.
The short answer
Choose uPVC if you want the best thermal performance per pound spent, your windows are standard domestic sizes, and you are replacing a whole house on a defined budget.
Choose aluminium if you want slim frames and maximum glass, you have large or unusually shaped openings, you want a specific colour, or you are glazing a contemporary extension where the frames will be seen.
Everything below is the detail behind that.
Cost
Aluminium typically costs 40% to 70% more than uPVC for an equivalent window. On a single unit that might be a few hundred pounds; across a whole house it is often the difference between £7,000 and £12,000.
| Window | uPVC (fitted) | Aluminium (fitted) |
|---|---|---|
| Standard casement | £450 – £750 | £700 – £1,150 |
| Large casement with opener | £650 – £1,000 | £950 – £1,500 |
| Three-sided bay | £1,800 – £3,200 | £2,800 – £4,500 |
| Whole three-bed semi | £5,500 – £9,500 | £9,000 – £15,000 |
A common compromise is to mix the two: aluminium on the rear extension and the openings people notice, uPVC on bedrooms and side elevations. There is nothing wrong with doing that, provided the colours are matched properly.
Thermal performance
uPVC is a natural insulator. Aluminium is a metal and conducts heat readily, which is why 1980s aluminium windows streamed with condensation. Modern aluminium solves this with a thermal break — a polyamide barrier between the inner and outer sections of the profile.
The result is that a good thermally broken aluminium window performs close to a good uPVC one, but uPVC still tends to win slightly on frame U-value at the same price point. Once the glass is factored in, the whole-window difference between the two is usually small — on the order of 0.1 to 0.3 W/m²K.
Put plainly: nobody has ever noticed the thermal difference between a modern aluminium window and a modern uPVC one by standing next to it. They have noticed the difference in frame width.
Sightlines and glass area
This is where aluminium wins clearly. Because the metal is stronger, the profile can be much narrower for the same structural performance. Typical frame sightlines run around 45mm to 60mm in aluminium against 70mm to 100mm in uPVC.
On a large window that difference is cosmetic. On a small one it is significant — a bathroom window with a 100mm uPVC frame can lose a quarter of its glass area compared with an aluminium equivalent, and the room feels darker for it.
Strength and maximum sizes
uPVC profiles need steel reinforcement inside the chambers to span large openings, and there is a practical ceiling on how large a single uPVC unit can go before it needs a transom or mullion breaking it up.
Aluminium spans further unaided. For a full-height window, a wide sliding door or a shopfront, aluminium is often the only realistic option. If your design depends on one enormous uninterrupted pane, that decision is effectively made for you.
Lifespan and maintenance
Both materials are low-maintenance. Neither needs painting.
uPVC lasts around 20 to 25 years in service. Its failure modes are discolouration on south-facing elevations, and gaskets and hardware wearing before the frame itself does.
Aluminium lasts 30 to 40 years or more. A quality powder-coated finish holds its colour extremely well, and the failure mode is usually a mechanical one — a hinge or a roller — rather than the frame degrading.
For both, clean the frames a couple of times a year, keep the drainage slots clear, and put a drop of light oil on the hinges annually. That genuinely is the whole maintenance regime.
Colour and finish
Aluminium is powder-coated, so any RAL reference is available, including matt and textured finishes, and different colours inside and out. The finish is baked on and does not fade appreciably.
uPVC comes in white as standard, with woodgrain and coloured foils laminated onto the profile. The range is wide and modern foils are convincing, but it is a finite catalogue rather than a colour chart, and dark foils on a hot south-facing wall can be more prone to visible ageing over decades.
Noise performance
Frame material has far less influence on noise than the glass does. Whichever you choose, acoustic performance comes from laminated glass, asymmetric pane thicknesses and good perimeter sealing.
If noise is your main problem, spend the money on the sealed unit specification rather than on upgrading the frame material. A uPVC window with proper acoustic glass will outperform an aluminium window with standard units every time.
Resale value and kerb appeal
Estate agents consistently report that new windows help a sale, mostly because they signal a maintained property. Whether aluminium adds more than uPVC depends heavily on the house.
On a contemporary property or a modern extension, slim dark aluminium frames read as a premium detail. On a Victorian terrace in a street of white uPVC, black aluminium can look out of place, and a flush-casement uPVC window with a heritage bar layout will suit the frontage far better.
Which should you choose?
| Your priority | Better choice |
|---|---|
| Lowest cost for the whole house | uPVC |
| Maximum glass, minimum frame | Aluminium |
| Best thermal performance per pound | uPVC |
| Very large or wide openings | Aluminium |
| A specific or unusual colour | Aluminium |
| Period property in a traditional street | uPVC flush casement or timber |
| Contemporary extension | Aluminium |
| Longest service life | Aluminium |
| Reducing traffic noise | Either — spend on the glass |
If you are still undecided, the most useful thing you can do is see both in daylight at full size. Photographs flatten the difference in frame width, which is the single characteristic most likely to change your mind either way.
Frequently asked questions
No. uPVC insulates better as a material. Thermally broken aluminium closes most of the gap, and once the glass is included the whole-window difference is small.
Non-thermally-broken aluminium did, badly. Modern thermally broken profiles behave much like any other frame — condensation usually points to humidity and ventilation rather than the frame.
Yes, and many people do — aluminium where frames are prominent, uPVC elsewhere. Match the colours carefully so the elevations read as deliberate rather than piecemeal.
Usually neither by default. Conservation officers often want timber or a flush casement that closely matches the original sightlines; check with the local authority before ordering.
Not significantly. Most repairs are hardware — hinges, rollers, handles — and those costs are broadly similar. Frame damage is rarer in aluminium because the material is tougher.
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