Foam Cut to Size, Foam can be easily cut to size using a few different tools, depending on the thickness and density of the foam. For thin foam, a utility knife can be used to cut through the foam. Make sure the blade is sharp, and cut slowly and steadily, using a straight edge or ruler to guide the knife along the cutting line. Before cutting, make sure to measure and mark the foam with a ruler and pen, and wear protective gloves and eye wear to prevent injury. Also, be sure to work in a well-ventilated area, as cutting foam can produce fine dust particles that can be harmful if inhaled.