Weekend-Racer.com highly recommends that all auto race drivers wear fire resistant underwear and undergarments to enhance the fire protective qualities of your racing suit. The FIA had stated that fireproof underwear can add as much as 50% to the time to burn.
Most suits are SFI 3.2A/5 rated, this rating yields only 10 seconds of protection before you start to resemble bacon. By adding a layer of fire resistant underwear made for motorsports will increase the time you have to get out of the car if it is on fire.
We're guessing that skin grafts are really uncomfortable... Underwear that have fire retardant properties is worth the added sweat!