Coir fiber is a good material for a crib mattress insulator pad as it is strong, firm, and durable. Fiber wrap or rag or ‘shoddy’ pads are also used and are cheaper and, some argue, just as effective. Woven polyester pads are liable to form pockets over time and should be avoided as these may create a safety issue for infants. Hard, pressed felt is also used as an insulator and can be an excellent material choice.