These winter hard hat liners have a 100% cotton twill shell with a sherpa lining. The cotton twill and binding are flame retardant until washed. This winter hard hat liner also has two built-in pockets which hold HOT RODS® Toe Warmers warming packs. The warming packs will stay warm for 7 to 11 hours. (Sold Separately). Occunomix winter hard hat liners are manufactured with a short elastic strip in the forehead area to keep the liner snug against the face. Other winter liners do not have this feature.