Thermally broken aluminum windows

Aluminum conducts heat about a thousand times better than the insulating glass it holds. A thermal break is the part that interrupts that path — and "thermally broken" on a datasheet covers everything from a serious polyamide strut to a token strip, so the number that settles it is the certified whole-window U-factor.

Key facts

Break material: Glass-reinforced polyamide (nylon PA66) strut — structural, low conductivity — Source: Manufacturer’s published configuration details
Best certified U-factor, thermally broken aluminum: 0.16 Btu/h·ft²·°F — Source: NFRC CPD SHN-M-21
What NFRC rates: The whole window — frame and glass together, not centre-of-glass
Certified product lines we hold: 44 product lines, 2,485 rated configurations — Source: NFRC Certified Products Directory, retrieved 2026-08-01
Where aluminum beats vinyl: Strength — larger glass areas and slimmer sightlines at the same span
Where vinyl beats aluminum: Frame conduction. Our best UPVC line certifies 0.14 Btu/h·ft²·°F — Source: NFRC CPD SHN-M-24

What the break physically is

The frame is extruded as two separate aluminum sections, inner and outer, joined by a strut of glass-reinforced polyamide. Our partners use nylon PA66: rigid enough to carry structural load, poor enough at conducting heat to interrupt the bridge. The inner face is now thermally separated from the outer face.

The consequences a building actually feels are a lower U-factor, a warmer inner frame surface, and a much higher condensation resistance number. That last one is what occupants notice — condensation on the inside of a frame is rarely a glass problem, it is usually the frame conducting.

The certified numbers, and what they are in

We hold 44 certified product lines in the public NFRC directory, covering 2,485 individually rated configurations. The best whole-window U-factor across the thermally broken aluminum lines is 0.16 Btu/h·ft²·°F; the best across every material we supply is 0.14, on a UPVC line.

Those are US units. If you are working from a European or Australian datasheet, multiply by 5.678 to compare — 0.16 Btu/h·ft²·°F is about 0.91 W/(m²·K). Mixing the two silently is the most common way a window gets specified five times better than it is.

Best thermally broken aluminum	0.16 Btu/h·ft²·°F — CPD SHN-M-21
Best of any material we supply	0.14 Btu/h·ft²·°F — CPD SHN-M-24, UPVC
Certified lines / configurations	44 lines · 2,485 rated configurations

How to interrogate a thermal-break claim

Ask what the strut is made of and how deep it is. Ask for the whole-window U-factor rather than a centre-of-glass figure, because centre-of-glass conveniently omits the frame you are asking about. Then ask for the NFRC CPD number, which settles it: a whole-product rating in a public directory cannot be argued with.

A supplier who can answer the first two and not the third is telling you something. Ask us for the CPD number covering your system and check it yourself.

Products this applies to

Every product below is in the live catalogue with its own specification table.

Signature Slimline Tilt & Turn Essential Tilt & Turn Essential Casement Signature Wood-Clad Tilt & Turn

Questions we are actually asked

Are thermally broken aluminum windows as efficient as vinyl?

Not on frame conduction alone — vinyl is a poorer conductor, so a vinyl frame starts ahead, and our best UPVC line certifies 0.14 against 0.16 for the best aluminum. Aluminum wins on strength, which is why it carries far larger glass areas and much slimmer sightlines. A thermally broken aluminum window with good glazing closes most of the gap on whole-window U-factor.

What is polyamide PA66 and why is it used?

A glass-reinforced engineering nylon. It is used because it does two contradictory things at once: it is stiff and strong enough to be a structural part of the frame, and it conducts heat poorly enough to interrupt the thermal bridge.

How do I verify a U-factor you quote?

Ask for the NFRC CPD number covering the system and configuration you are specifying, then look it up in the NFRC Certified Products Directory yourself. We will confirm the number in writing before you specify from it.