Fibre-Metal Brand WNDW 4178 CLEAR. Fibre-Metal face shield windows are injection molded from propionate, which is superior to other window materials in every significant performance characteristic. They are preformed at the factory to the exact curve of our crown protectors for easy installation, an exact fit and a perfect seal against dust, dirt and debris. All HIGH PERFORMANCE windows are thick for an extra margin of protection, yet they cost no more than ordinary.