Fire retardant fabrics, of which there are a number, are fabrics which are more resistant to fire than normal fabric. Fire retardant tarps and other products produced from similar fabrics become the way they are either through a chemical treatment of the fibers or the fibers are made to be fire retarding right from the start of production of the fabric.
What’s important to understand in a discussion about either fire retardant material or fire resistant material is that they are not “fire proof.” The material may have a considerably slower rate of burn, but if left long enough they will burn. If these materials are exposed to a fire long enough, odds are they will no longer be usable. The whole objective of using fire resistant or fire retardant tarps is to reduce the spread of a fire; it does not matter if the material is destroyed in the process.
Although rarely used, natural fabrics such as cotton can be chemically treated to make them fire resistant; the chemical reduces the flammability of the fabric. The chemical that is used is applied topically and react with the gases and tars that are a natural component of cotton, when the chemical reacts with these naturally occurring gases and tars the fabric chars rather than break into combustion.
Natural fabrics are rarely used because fire retardant materials are normally subjected to arduous duty. Fabrics that are made especially to be a fire retardant are more durable because they are simply not treated chemically. The material that is popular for use as fire retardant canvas tarps for example is high density polyethylene, when the material is produced the fire resistant properties are built right into the fibers.
Because the materials that are manufactured exclusively for this purpose have their properties ingrained during manufacture they are far more effective than topically protected fabric which over time may very well lose their ability to resist fire at all.
One of the primary uses for fire retardant fabric is in fire fighters suits. These suits are made with exotic materials which have the fire resistant properties built in at the molecular level. The materials used for these suits not only resist fire, they do not char when the fire fighter is engulfed in flame.