Thermal break: what it is and when it counts

A thermal break reduces the thermal connection between the outer and inner side of the profile.

In thermally broken systems, the inner and outer aluminium sections are joined through a material of lower thermal conductivity. This limits the flow of heat through the frame.

The actual performance, however, is assessed on the complete window. That is why we look at the Uw, which takes the frame, the glazing unit, the spacer and the geometry together.

Aluminium conducts heat very well — which makes it an excellent structural material and a poor insulator. A thermal break separates the outer from the inner shell of the profile with polyamide bars, usually PA66 with 25% glass fibre, which are a load-bearing part of the profile and not a filler. The word is not one category, though: the width of the polyamides and the geometry of the chamber decide the U_f, and between two thermally broken series the difference can be larger than the difference between double and triple glazing. That is why real performance is judged on the whole window, through the U_w.

What exactly is broken

Aluminium conducts heat very well — which makes it an excellent structural material and a poor insulator. A thermal break separates the outer and inner shell of the profile with polyamide strips, usually PA66 with 25 % glass fibre, which are a load-bearing part of the profile and not merely a filler.

“Thermally broken” is not one class

The width of the polyamide strips and the geometry of the chamber determine U_f. Between two thermally broken series the difference can be larger than the difference between double and triple glazing. So the word on its own says nothing; the number does.

A thermal break is not only about consumption. It keeps the inner face of the frame warmer, and that is usually where surface condensation starts — in the cold corner, not on the glass.

Thermal break: what it is and when it really counts

What exactly is broken

“Thermally broken” is not one class