Usually we think of composite structures only being found on boats. Here in Copenhagen is a composite window structure in a hotel. Probably they are pultrusions. Horizontal one is a solid fiberglass flange.
Vertical is fiberglass box section. They are much less of a heat sink than metal framing would be. Composites go corporate!
You can get pulltrusions of glass at the HD store, and while a heavy thing to go wild with, they have some useful applications armouring rub areas and configuring flanges where drop boards go in, etc…
HD store? Home Depot?