Fiberglass windows are beautiful to behold, and they’re tough enough to stand up to Wisconsin weather, year round. They also have a slimmer profile than wood or vinyl windows, for a better outside view. Some of their benefits include the fact that they’re waterproof, unaffected by temperature — and deliver approximately 8X the strength of vinyl. Thus far in our fiberglass windows series, we’ve covered Pella fiberglass windows. In this installment, we shift our attention to Marvin’s line of fiberglass windows. But first, let’s review the two types of fiberglass that Marvin utilizes in their windows so you have a better understanding of which is best for your home, and your budget. Ultrex® Fiberglass & High-Density Fiberglass Over 25 years ago, Marvin launched Ultrex Fiberglass for use with windows and doors. Since then, they’ve advanced their technology and added a High-Density Fiberglass offering that’s stronger than Ultrex. That said, both types of Marvin fiberglass provide outstanding durability, energy efficiency and strength.  Ultrex Fiberglass is utilized for the exterior of Marvin’s Elevate fiberglass windows and doors,