The headline differences
| Factor | Aluminium | PVC |
|---|---|---|
| Frame sightline | 50–80mm | 100–125mm |
| Max pane width | 1,200mm+ | 900mm typical |
| Frame lifespan | 25–30 years | 10–15 years |
| Frame guarantee (typical) | 10–20 years | 10 years |
| U-value (whole window) | 1.4–1.6 W/m²K | 1.4–1.7 W/m²K |
| Pane weight tolerance | High | Lower |
| Colour stability outdoors | Excellent | Fades on south-facing |
Sightlines — the visible difference
Walk past a finished installation and the giveaway is the frame width. Aluminium's tensile strength means you can carry the same pane on a much thinner profile — typically 50–80mm versus 100–125mm for PVC. Across a 4-pane bi-fold that's an extra 200mm of glass area. On a rear extension where the whole point is to dissolve the boundary between inside and out, that matters.
Pane size and structural reach
PVC's lower stiffness limits practical pane sizes. Most PVC bi-folds use panes around 800–900mm wide; pushing beyond that introduces deflection and risk of seal failure. Aluminium routinely carries 1,000–1,200mm panes and several premium systems will go to 1,200mm+. For openings beyond about 3m wide, aluminium is the only sensible choice.
Lifespan and lifetime cost
This is where the budget calculation flips. PVC frames have a usable life of 10–15 years before UV degradation, gasket failure and hardware wear catch up. Aluminium runs 25–30 years on the frame with sealed-unit replacement at year 20–25.
Annualised over the working life of the frame, aluminium typically works out cheaper per year despite the higher upfront cost — and that's before you count the installation labour cost of replacing the PVC twice.
Thermal performance
Modern thermally-broken aluminium and quality PVC are within touching distance on U-value — typically 1.4–1.7 W/m²K depending on glass spec. Both meet current Building Regulations Part L. The real thermal advantage of aluminium isn't the frame material itself, it's that you can fit larger glass area, which performs better than frame on solar gain.
Colour and finish
Aluminium powder-coat is dyed through the coating process and bonded to the metal. South-facing aluminium frames in Essex are still colour-true at year 15. PVC is typically through-coloured (white) with film-laminated foils for grey, black, or wood-effect finishes. The foils are improving but UV exposure on south and west elevations can cause noticeable fading by year 8–10.
When PVC is genuinely the right choice
- 2-pane installations under 1.8m wide — sightline difference is less visually obvious, and pane-size limits don't bite.
- Properties you're selling within 5 years — buyer perception of "double doors" is what matters, not 25-year lifespan.
- Rentals or commercial premises where reliable budget specification trumps premium spec.
- Replacement of an existing PVC bi-fold where matching adjacent frames matters more than upgrading.
When aluminium is non-negotiable
- Openings over 2.4m wide
- South or west-facing elevations
- Premium new-build extensions where neighbouring properties have aluminium
- Coastal or estuary properties (with marine-grade powder-coat)
- Anywhere you want slim sightlines as a design choice
For full configurations on both, see our bi-fold doors service in Essex, or the broader doors category page.