Thermal Break: Why Aluminium Windows Sweat Without One
A thermal break is an insulating strip — usually polyamide — bonded between the inner and outer halves of an aluminium profile, so heat cannot conduct straight through the frame. Without it, the frame is a continuous metal bridge between outside and inside.
By Dhruv Agarwal · · 2 min read
Why it matters on a project
Aluminium is roughly a thousand times more conductive than the polyamide strip that breaks it. That single fact is why an unbroken aluminium frame behaves like a heat pipe through the wall — and why, in a chilled office in a humid Indian summer, water appears on the inside face of the frame while the glass stays clear.
Occupants read that as a leak. It is not; it is condensation on a cold metal surface, and it is a specification decision made months earlier.
How it is specified in practice
| Parameter | Typical position | Why |
|---|---|---|
| Break material | Polyamide 6.6, glass-fibre reinforced | Low conductivity, and strong enough to be structural |
| Break depth | Commonly 14-34mm | Deeper break, better performance and higher cost |
| Assembly | Rolled-in and knurled, factory | The composite must act as one section structurally |
| Alloy | 6063 T6 | Standard architectural extrusion alloy |
| Gasket | EPDM | Durable under UV and thermal cycling |
| Verification | System U-value from the system supplier | Frame performance is a tested property, not a claim |
Common mistakes
- Specifying thermally broken glass and a plain frame. Paying for high-performance DGU and then bridging the assembly with bare aluminium wastes most of the benefit at the frame.
- Assuming it is only for cold climates. In India the driver is usually cooling load and condensation control, not heating.
- Ignoring the break depth. "Thermally broken" covers a wide performance range. A 14mm break and a 34mm break are not the same product.
- Breaking the frame and forgetting the fixing. Steel brackets bridging around the break reintroduce the path the break was meant to interrupt.
- Mixing systems. Profile, gasket, hardware and drainage are designed as one assembly. Substituting one part of it invalidates the tested performance.
Where Hagerstone uses it
Our fenestration work runs on engineered systems rather than assembled parts. As a strategic partner, Winda Window Systems supplies aluminium and uPVC window and door systems manufactured in Ludhiana as a single engineered assembly — profile, hardware, gasket, drainage and glass — using 6063 T6 alloy, EPDM gaskets and EN-certified hardware.
Standards referenced
Fenestration U-value requirements by climate zone are set by ECBC 2017. Architectural aluminium extrusion alloy and temper are covered by IS 733.
Standards referenced
- ECBC 2017 — Building envelope — fenestration U-value
- IS 733 — Wrought aluminium alloy bars, rods and sections