How it works.
The frame is extruded in two pieces, one for the outdoor side and one for the indoor side. A strip of insulating material is rolled into a groove between them, mechanically locked, and the whole assembly behaves as one frame structurally but two frames thermally. Heat hitting the exterior aluminum cannot conduct across to the interior aluminum because the insulating strip stops it.
The most common thermal-break material is PA66 polyamide, a glass-fiber reinforced polymer that holds its dimensional shape under temperature swings and bonds reliably with the aluminum extrusion. Some legacy systems use polyurethane foam, which is lower performance but cheaper.
Why it matters.
A non-thermally-broken aluminum frame can hit a U-factor of 1.5 to 2.0, which is barely insulating; the frame is the weak link in the whole window. A thermally-broken frame brings the same window down to a U-factor of 0.25 to 0.35 territory, competitive with vinyl, and pairing it with a triple-pane LowE argon IGU pushes it lower still.
Without a thermal break, condensation will form on the interior frame any time the outdoor temperature drops far enough. That is the dripping-window problem from older aluminum installs. The thermal break fixes it because the interior aluminum never gets that cold.
Common questions.
- What is a thermal break in a window?
- A thermal break is an insulating barrier set inside an aluminum window frame between the exterior aluminum and the interior aluminum. It stops heat from conducting through the frame, which is what makes aluminum windows competitive with vinyl on energy performance.
- Do all aluminum windows have a thermal break?
- No. Non-thermally-broken aluminum windows still exist for warehouse, garage, and budget commercial applications. For any residential project or any climate that gets cold, the thermal break is the version worth buying.
- How much does a thermal break improve performance?
- A thermal break can cut frame U-factor by roughly 70 percent compared to a non-thermally-broken aluminum frame, and it eliminates the interior condensation problem that older aluminum installs had in cold weather.
Project in motion
Specifying thermally-broken aluminum?
Every Crateworks window and exterior door uses a PA66 polyamide thermal break in a 6063-T5 aluminum frame. Send your project for a quote on the spec.