2. Measure the circumference of your head. You’ll know the exact width of foam or cardstock you’ll need by dividing that number in half and adding 1 inch. Based on your individual measurement, mark and cut the determined amount of foam or cardstock from your sheet. (So, if your head’s circumference is 22 inches, divide 22 by two and add 1 inch. You get 12, and now know that you’ll be using a piece that measures 12 inches across.) Additionally, make a mark two inches from the top that runs the length of the foam or cardstock. Cut this section off, as well. Using these measurements, you will now have a 10-inch by 12-inch sheet.