Now the template design is ready to be transferred to the shroud material. Although you can use aluminum, the best choice is a sheet, or roll, of plastic, which is available from most racing supply stores. The plastic is actually a high-density polyethylene that's flexible and can usually stand up to a few impacts. Sheets are normally 48x96 inches and 0.100-inch thick, while rolls are 20-24 inches wide, 0.070-inch thick and about as long as you want. Which you use is up to you.