Textiles for use indoors are soaked in fire-retardant solutions made up mostly of boric acid and borax. Textiles for outdoors are soaked with chlorinated paraffin, chlorinated synthetic resins, or chlorinated rubber. The standard for effectiveness of these treatments is the weight of chemicals remaining after the materials dry. Large areas of textiles are brushed or sprayed, but they gain little resistance against severe fire exposure; the treatment is mainly a guard against lit cigarettes and short exposure to flame.
Rain, washing, or dry cleaning tends to leach the chemicals from the fabric; therefore latex is often added to waterproof the material. At one time asbestos could be mixed with natural fibers to increase their fire resistance, but now only glass or ceramic fibers are permitted. The fire resistance of a textile is generally expressed in hours of endurance to a standard temperature furnace.