Fibrex material is a proprietary composite developed by Andersen and is exclusive to their products. It’s made up of 40% wood fiber and 60% thermoplastic polymer. Most of the Fibrex material used in constructing these windows is reclaimed, making it sustainable and earth friendly. It also reduces volatile organic compounds (VOC) gas emissions because no painting or wood treatments are needed. Andersen Fibrex material is amazingly tough and will not blister, peel, flake, or fade — even under extreme weather conditions.