Despite the header, we are as serious as cancer about this hard hat liners job. The most common places for sun-related skin cancer is your neck and ears. If you are working in the sun all day, it is important to protect yourself. This warm weather FR hard hat liner is safe to wear directly against your skin, it is soft, thin and can be used as a cooling towel under your hard hat.
If you would normally wear a baseball cap to keep the sun off your head, then you should consider this for when you wear a hard hat. NFPA states "Clothing and other apparel (such as hard hat liners and hair nets) made from materials that do not meet the requirements regarding melting, or made from materials that do not meet flammability requirements shall not be permitted to be worn.” In other words, the FR Hard Hat Liner will not further "contribute to the extent of an injury (OSHA).