As you were shopping for a new racing suit you kept seeing words such as FR cotton, Proban®, Pyrovatex®, and thought to yourself, what does that mean? These are generally the least expensive types of flame resistant materials. The cotton fibers absorb and retain fire retardant chemicals in the treatment process. In general, they will retain the fire retardant properties beyond the point when the fabric is worn out. Because it is a cotton base, the material has excellent breathability, does not cause itching or irritation and is reasonably durable. It is also very stable in direct contact with flame, with no tendency to melt or shrink. These materials are common in a SFI 3.2A/1 rating but can be combined with other materials to achieve a higher rating.
One of the other most common materials is Nomex®, which is a fire-retardant version of Nylon, developed by DuPont®. Nomex III® is a combination of Nomex® fibers and Kevlar® fibers. This combination is very stable in heat and flame and is very durable. It tends to have a higher TPP for its weight than the cotton materials. Cost of Nomex® varies widely, but is always considerably higher than cotton materials. Suit liners may consist of a layer of Nomex® knit material. The combination of an outer layer of Nomex® and a liner of Nomex® knit offers a lighter suit that still achieves an SFI 3.2A/5 rating.
To put it in layman's terms, the FR cotton, Proban®, Pyrovatex® started out as regular cotton material that has been treated with a fire retardant chemical. Nomex®, on the other hand is inherently in itself fire retardant and not dependent upon chemical treatment. Regardless of the material you decide to go with, as shown in the video, it is strongly recommended that you add a layer of fire retardant underwear; it could make the difference in walking away from a fire and being carried away.