Flame-resistant clothing is made from fabrics that are heavy and tightly woven. Many synthetic fabrics are also flame resistant. Flame-retardant chemicals sometimes are added to clothing, to make it particularly resistant to fire.
Wool is naturally more fire-resistant than other fabrics. It does not catch fire easily and does not burn as quickly as other materials. The tighter and heavier the wool, the more fire-resistant it is.
Synthetic fabrics, such as nylon and polyester, take a longer time to ignite than cotton, linen or silk. Once these synthetic fabrics are afire, though, they tend to melt. The tighter and heavier the weave of the synthetic fabric, the more flame-resistant it will be.
Fire-resistant coating is sometimes added to a fabric to decrease the likelihood that it will catch fire and burn. Specialty fabric companies make fabrics with these chemicals added.