Short answer: aluminium conducts heat very well, so an aluminium profile that runs straight from outside to inside carries heat and cold through the door. A thermal break, an insulating strip between the outer and inner profiles, cuts that path. You need one when the project has an energy target or code limit for doors, when winters are cold, or when the inside is air-conditioned against strong outside heat. It is one part of the door's U-value, along with the leaf core, the seals and any glass.
Why does aluminium need a thermal break?
Metals conduct heat. Typical figures for thermal conductivity:
| Material | Thermal conductivity |
|---|---|
| Aluminium alloy 6063 | about 200 W/m·K |
| Carbon steel | about 43–50 W/m·K |
| Stainless steel 304 | about 14–15 W/m·K |
| Polyamide 66 with 25% glass fibre (thermal-break strip) | 0.30 W/m·K |
A continuous aluminium profile is a thermal bridge. On a cold day the inside face of the frame gets cold; on a hot day it carries heat in. A polyamide strip between the two halves of the profile makes a much poorer path for heat.
When does it matter, and when does it matter less?
It matters most when:
- The project has to meet a U-value, for example a code, an energy rating or a specification.
- Winters are cold, and condensation on the inside of the frame would be a problem.
- The house is air-conditioned and the door faces strong sun.
It matters less where the door is sheltered in a lobby or porch, or where the climate is mild. Even then, seals matter, because air leaking round a door carries heat too. Our guide on how pivot doors are sealed covers that.
What else decides how well a door insulates?
The frame is only part of it. The door’s overall U-value also depends on:
- The leaf. Our leaves are built in layers: the face, a galvanised steel sheet, an aluminium frame with an aluminium honeycomb core, a second galvanised steel sheet and the inside face.
- The seals round the leaf and at the threshold.
- Any glass, and its edge spacer.
- The installation: the gap between frame and wall, and how it is filled and sealed.
Why do cold frames cause condensation?
Condensation forms when a surface is colder than the dew point of the air next to it. In a heated house in winter, a cold aluminium frame or threshold can drop below the dew point of the indoor air, and water appears on it. A thermal break keeps the inside part of the frame warmer, which reduces the risk.
How is a door’s U-value worked out?
| Method | What it does |
|---|---|
| ISO 10077-1 | Simplified calculation of the U-value of whole windows and doors |
| ISO 10077-2 | Numerical calculation of frame profiles, where frame meets glass or panel |
| EN ISO 12567-1 | Hot-box measurement of complete windows and doors, including door leaves |
| ANSI/NFRC 100 | Computer simulation of U-factor, used in North America |
Ask for the method, the size of door it applies to, and the report.
What do ENERGY STAR and the Australian NCC ask for?
- ENERGY STAR (United States), version 7.0: opaque doors need a U-factor of 0.17 or lower; doors with up to half glass, 0.23 or lower.
- ENERGY STAR Canada, version 5.0: doors need a U-factor of 1.22 W/m²·K or lower (or an energy rating of 34 or more), plus an air-leakage limit. A version 6 draft was published in October 2026.
- Australia, NCC 2022: for houses, external glazing is assessed under Housing Provisions Part 13.3, with the ABCB glazing calculator.
These are voluntary labels or code paths, not requirements for every door. Check what your project needs. Our thermal-break doors have PA66 polyamide insulating strips in the aluminium profiles, and this construction reaches a U-value of 1.0 W/m²K in our test report. It is not tied to one model, so any of our designs can be built with it. Ask us for a copy of the report; if your project needs a figure for a particular size or glass, ask early, and we can arrange a calculation or test with a lab, usually at the buyer’s cost.
Sources, checked October 2026: Technoform, polyamide insulating strip data and causes of condensation; Gabrian, 6063 aluminium properties; Engineering ToolBox, thermal conductivity of metals; FGIA, condensation; EN ISO 10077-2; EN ISO 12567-1; Intertek, ANSI/NFRC 100; ENERGY STAR, version 7.0 criteria letter; Natural Resources Canada, ENERGY STAR Canada specification; ABCB, Housing Provisions Part 13.3.
Quick answers
What is a thermal break in an aluminium door?
It is an insulating strip, usually glass-fibre reinforced polyamide, that separates the outer and inner aluminium profiles of a frame. Polyamide conducts heat several hundred times less than aluminium, so less heat crosses the frame.
When does a front door need a thermal break?
It matters most where there is a big difference between inside and outside temperature for long periods, in cold winters or in air-conditioned buildings in hot climates, and where the project has an energy target or a code limit for the door.
Do you publish a U-value for your doors?
Yes. Our thermal-break construction has PA66 polyamide insulating strips in the aluminium profiles and reaches a U-value of 1.0 W/m²K in our test report. Any of our designs can be built with it; ask us for a copy of the report.