Polypropylene - Proteus? O&P Grade SheetOrthopedic polypropylene sheets are used for orthotic & prosthetic devices. Because people come in all different shapes and sizes, orthotic and prosthetic devices must be custom fit - and that's where Proteus? O&P Grade comes in. Proteus? O&P Grade maintains the rigidity and durability required by the orthotics and prosthetics industry, while exhibiting top thermoforming performance. Proteus? O&P Grade is a "natural" color and available in 48" x 96" sheets with gauge sizes ranging from 1/16" to 1/4".