Cotton/poly fabric blends tend to be more fire resistant than 100 percent cotton or 100 percent polyester fabrics. Cotton catches fire easily, while polyester fabrics tend to melt when exposed to heat.
Regulations for Children's Sleepwear
According to U.S. Product Safety Commission, Office of Compliance, Children's Sleepwear Regulations 1, 16 C.F.R. Parts 1615 & 1616, children's sleepwear must pass flammability tests. A blend of 80 percent cotton and 20 percent polyester was found to smolder or develop small holes rather than burst into flame.
Saying that a fabric is flame resistant is not the same as saying it is fireproof. Polyester-based fabrics seem to be less likely to burst into flame than cotton. However, once the polyester fabric is hot, it will melt, thereby causing painful burns on whatever part of the body the fabric is touching.
Fabric Fire Safety
Adding flame-retardant chemicals to the fabric can increase its fire resistance. Making garments in styles that fit close to the body without dangling ornaments can prevent accidentally setting fire to garment parts.
Weave and Fabric Type
Thick heavy weaves of cloth with smooth textures tend to be less flammable than light, gauzy fabric or fabric with a fuzzy nap, such as flannel, notes Fabrics.net.