uPVC or aluminum. Where each one belongs.

Neither material is better everywhere. Aluminum is stiff and slim, and it takes almost any color. uPVC insulates well, seals tightly and needs little care. On a typical mid-rise residential building, the punched window openings suit uPVC, and the entrances, storefronts and glass walls suit aluminum. Many good buildings use both.

What each frame is.

Aluminum is an extruded metal section. Metal conducts heat easily, so an exterior aluminum frame needs a thermal break: a strip of low-conductivity material that separates the inside metal from the outside metal. Aluminum without a thermal break belongs indoors. How good the thermal break is decides how good the window is.

uPVC is an extruded profile of rigid PVC, divided into chambers, with steel reinforcement inside. The plastic insulates and seals. The steel carries the load. The corners are welded into one piece.

Side by side.

	uPVC	Aluminum
Heat	The material itself insulates, and the chambers add to it	The metal conducts. Performance depends on the thermal break
Stiffness	Comes from the steel inside the profile	Comes from the metal itself, so sections can be slimmer
Sightlines	Wider frame	Slimmer frame, more glass
Color	White, or a laminated finish from a set range	Powder coat or anodizing in almost any color
Corners	Welded	Mechanically joined and sealed
Salt air	Does not corrode	Needs the right finish, and washing, near the coast
Movement with temperature	Moves more	Moves less
Recycling	Can be reprocessed. Collection is less developed	Recycled widely, without loss of quality

Heat.

The NFRC U-factor describes the whole window, frame included. On a punched window the frame is a large share of the area, so the frame material shows up in the number.

A thermally broken aluminum window can reach good U-factors. It takes a wide, well-designed break to get there. A uPVC frame starts from a material that does not conduct much heat, which is why it reaches low whole-window numbers with ordinary glass. As a reference point, the Vistaza Vi5 casement is NFRC-certified at U 0.30 with plain insulated double-pane glass and an aluminum spacer. The Vi6 casement is certified at U 0.17 with a krypton-filled triple-pane and a warm-edge spacer.

A frame that stays warmer on the room side also collects less condensation in winter.

When you compare the two materials, compare certified whole-window values for the same type and a similar glass. Center-of-glass numbers hide the frame. There is more on this in certified or simulated U-factor.

Strength.

Aluminum is the stiffer material. That is why curtain wall, window wall and storefront are made from it, and why it suits long spans and very large lites.

A uPVC frame gets its stiffness from the steel inside it. Whether that is enough is not a matter of opinion. Both materials are tested to the same standard, NAFS, and earn the same classes and grades. The Vistaza Vi6 casement is rated AW-PG100 under Intertek report S3614.03-525-44. A rating applies up to the size that was tested. If an opening needs a span beyond what a reinforced uPVC frame has been tested to, that opening is an aluminum opening.

Sound.

Glass does most of the work. Seals do most of the rest. The frame material is a small part of the result, and either material can be quiet with the right glass and compression seals that close tightly.

What matters is that the rating comes from a test of the whole window. The Vi6 casement reaches STC 47 and OITC 40 with a laminated acoustic triple-pane, under report J4759. Ask any supplier, in either material, for the same kind of report.

Color, upkeep and the coast.

Aluminum wins on color freedom. Powder coat comes in nearly any RAL color, and anodizing gives a metal finish that nothing else matches. uPVC is white, or carries a laminated finish chosen from a set range. Vistaza's range is on the colors page.

Both materials need washing and little else. Near the sea, uPVC does not corrode. Aluminum does well there too, but it needs a finish chosen for salt air and regular washing. The hardware is metal in both cases and needs the same care.

Movement.

uPVC expands and contracts more with temperature than aluminum does, and a dark frame in full sun gets hot. This is a detailing matter. The perimeter joint and the installation method have to leave the frame room to move, and the shop drawings should show how.

Cost.

For a punched residential window, uPVC usually costs less than a thermally broken aluminum window of similar thermal performance. The gap changes with size, color and glass, so price both against the same schedule.

How to choose.

Choose aluminum when:

• The opening is an entrance, a storefront, a curtain wall or a window wall.
• The design depends on the slimmest possible sightlines.
• The span or the lite is larger than a reinforced uPVC frame has been tested to.
• The color must be a specific RAL or an anodized finish.
• The design team requires non-combustible framing.

Choose uPVC when:

• The openings are punched windows and terrace doors in apartments, student housing or hotels.
• The energy target is tight.
• The street is noisy and the glass will be heavy.
• The site is near salt water.
• The owner wants the least upkeep across many units.

Pick the material by the opening, not by habit.

Vistaza works this way on its own projects. The windows and terrace doors are High Performance uPVC. The ground-floor entrances are aluminum storefront. If a project is truly an aluminum project, we will say so.

To see which series fits your openings, choose a window.