Curly Brunette Girl Posing At The Window

Steel - medium - superior - very low - high - >98% - typically welded at corner joints
Fiberglass - very good - very good(1) - very low - high - medium
(1) Vinyl and fiberglass frames perform well in accelerated weathering tests. Because vinyl is not as strong as other materials, some vinyl frames are reinforced with metal or composite materials to improve their structural strength.