Aluminium as a metal conducts heat very well indeed. For windows and doors that are not thermally broken this would severely affect the performance of the window during the winter and the summer months.
The thermal break in aluminium is a barrier that breaks the aluminium to aluminium contact from the inside to the outside of the window. In other words, your modern aluminium window is aluminium outside, a thermal barrier in between and aluminium inside. It simply separates the aluminium.
Our thermal break window uses polyamide plastic strip separating the internal and external faces of the aluminium. This has resulted in window profile being manufactured in separate extrusions to create the finished profile unlike before when it was extruded as one.