There are two main types of flame retardant fabrics: treated and inherently flame-resistant. Treated fabrics undergo a chemical treatment where flame retardant substances are applied to the fabric surface. Inherently flame-resistant fabrics, on the other hand, are made from fibers that possess natural flame resistance properties. Examples of inherently flame-resistant fibers include aramid fibers (such as Nomex and Kevlar) and modacrylic fibers.