Why do some vinyl windows yellow over time?
One major factor in vinyl integrity is whether or not a window is made of only virgin vinyl. Some manufacturers will heat up the vinyl resin to extrude a window frame and once the frame has been cut will remelt the scraps to extrude again. This compromises the vinyl integrity. Each time the vinyl is reheated at such extreme temperatures it becomes weaker and therfore susceptible to UV infiltration. Another major factor is whether or not the window manufacturer includes titanium dioxide in the vinyl. Titanium dioxide strengthens the vinyl to protect from UV infiltration.
