Reviewing the expansion and contraction chart below, vinyl windows expand and contract 8 times more than the glass they surround. Each and every day, the frames expand and contract 8 times more than the glass they surround. Over time the frame will pull away from the glass and cause seal failure, and the argon gas will leak out.
Fibrex only expands and contracts 4 times more than the glass that it surrounds, so it does do a better job than most other vinyl windows; however, it still expands and contracts 4 times more than the glass the frame surrounds.
Infinity from Marvin’s ULTREX® frames are as strong as steel and has never had a seal failure in over 20 years because the frames expand and contract at almost the same rate as the glass it surrounds, so the frames do not pull away from the glass, and the seals don’t break. The extra three layers of acrylic capping prevent color fade, chipping, peeling, and cracking.