Fibre-Metal faceshield 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 0.060Â3 thick for an extra margin of protection: yet they cost no more than ordinary 0.040Â3 thick windows.