Vinyl windows with frames made of uPVC (unplasticized polyvinyl chloride) extrusions insulated with a polyurethane core are much more energy efficient than wood, multi-chambered hollow vinyl, aluminum, and composite windows. Also make sure you look at the R-Factor of both glass AND frames. Remember, the greater the R-Factor the better the insulating value.

All Vanguard Windows are constructed with a polyurethane core.