Marvin Windows have several different options available, one of these options is their Fiberglass products. The Wood Ultrex windows are a Pultruded fiberglass exterior with a Pine wood cap stock interior. They have 6 exterior colors to choose from and 2 interior options. Ultrex Fiberglass clad wood windows and door are quite possibly the perfect materials for the NW environment. They are durable, strong, stable, low-maintenance and efficient. Integrity windows and doors made with Ultrex pultruded fiberglass outperform roll-form aluminum, vinyl, and vinyl/wood composites in virtually every measurable category. While other windows might bend, break, or crack over time, Integrity windows hold strong and perform under great stress without showing age or wear.