All fabrics will burn but some are more combustible than others. Untreated natural fibers such as cotton, linen and silk burn more readily than wool, which is more difficult to ignite and burns with a low flame velocity.
The weight and weave of the fabric will affect how easily the material will ignite and burn. Recommended fabrics are materials with a tight weave. Heavy, tight weave fabrics will burn more slowly than loose weave, light fabrics of the same material. The surface texture of the fabric also affects flammability. Fabrics with long, loose, fluffy pile or "brushed" nap will ignite more readily than fabrics with a hard, tight surface, and in some cases will result in flames flashing across the fabric surface.
Most synthetic fabrics, such as nylon, acrylic or polyester resist ignition. However, once ignited, the fabrics melt. This hot, sticky, melted substance causes localized and extremely severe burns. When natural and synthetic fibers are blended, the hazard may increase because the combination of high rate of burning and fabric melting usually will result in serious burns. In some cases, the hazard may be greater than that of either fabric individually.
Curtains, draperies and other articles in the home can have their burning rates reduced with flame retardants applied through chemical treatment. Such flame-retardant treatment after manufacturing is not recommended for clothing.
In terms of flammability, silk may be the worst with a high burning rate, which may be increased by the dyes and other additives to provide color.
Cotton and linen also have a high burning rate but this can be alleviated by the application of flame-retardant chemical additives.
Acetate and triacetate are as flammable or slightly less flammable than cotton. However, they can be made flame-retardant with chemical treatment.
Nylon, polyester and acrylic tend to be slow to ignite but once ignited, severe melting and dripping occurs.
Wool is comparatively flame-retardant. If ignited, it usually has a low burning rate and may self-extinguish.