The flammability of fabric can be drastically reduced through the use of fire retardants. Many natural fibers, including cotton, can be topically treated with a chemical that reduces the fabric’s flammability to the extent that it becomes nearly non-combustible. During a fire, the chemical reacts with the gases and tars generated naturally by the fabric, converting the gases and tars to carbon char, thus drastically slowing the fabric’s burning rate.
The ignition and burn factors of fabric are also affected by the weight and weave of the fabric. Lightweight, loose weave fabrics will burn more quickly than heavier fabrics with a tight weave. In addition, fabric flammability can also be affected by the fabric’s surface texture, with napped fabrics (such as velvets and velours) igniting more easily than fabrics with a smooth surface.
For textiles, the critical factor in determining flammability ratings for varying construction techniques is the availability of oxygen. Combustion is accelerated if air can permeate a fabric easily. The more loosely woven a fabric, the more combustible it is, and the faster the flame will travel over the surface of the fabric. For example, a lightweight tightly woven polyester fabric may be difficult to ignite, whereas a lightweight loosely woven (mesh) polyester fabric may fail flammability testing.
Fabrics with a raised fibre surface require special consideration. Fleece-style fabrics, flannelettes and terry towelling are some examples of construction which allow individual fibres or yarns to be exposed readily to accidental contact with ignition sources. This, combined with the fact that air readily penetrates and circulates around these loose fibres and yarns, increases the hazard level of raised fibre surface fabrics.
The flammability hazard with raised fibre surface fabrics involves the phenomenon called "surface flash" whereby a flame can travel rapidly over the fabric surface, singeing the fibre ends. This flash, in itself, may not be dangerous unless the intensity of the flame is sufficient to ignite the base fabric. In testing, this is known as timed surface flash with base burn.