Aluminum is the most common material for window frames in very large structures, especially in curtain wall facades. It is relatively inexpensive, is durable, and requires little maintenance. However it is a bad insulator, with very high thermal conductivity.

The aluminum forms the window frame, which is separate from the glazing. Its low maintenance requirements do not make the metal itself an effective thermal insulator.

A thermal break interrupts the conductive path through a metal frame. It can improve the performance of an aluminum window without changing the frame material to wood, vinyl, or fiberglass.