What is a thermal break?

A thermal break is a strip of insulating material — normally polyamide — set between the inner and outer halves of an aluminium frame so heat cannot conduct straight through the metal.

Why aluminium specifically needs it

Aluminium conducts heat roughly a thousand times better than uPVC. That is excellent in a saucepan and a serious problem in a window frame. Without a break, the frame is a continuous metal bridge from outdoors to indoors: heat pours out along it, and the inner face sits close to outdoor temperature and condenses.

How it is built

The frame is made as two separate extrusions. A polyamide strip is mechanically crimped or rolled into channels in both, locking them together into one rigid section that is structurally continuous but thermally split. Polyamide is used because it is strong enough to carry the structural load, insulates well, and expands and contracts at close enough to the same rate as aluminium not to work loose over decades.

What it is worth

The difference between a non-broken and a broken aluminium frame is the difference between a window that runs with condensation and fails modern standards, and one that reaches a whole-window U-value around 1.2 to 1.4 W/m²K and meets Part L. It is not a marginal upgrade — it is the single change that made aluminium a viable window material again.

Checking what you have

Open the window and look at the frame edge in section. A thermally broken frame shows a visible line of dark plastic running between the inner and outer metal. No line means no break, which means the window predates about 1990 and the condensation you are getting is structural.

Everything we supply in aluminium is thermally broken. There is no reason to fit anything else.