How is fireproof underpants a spin off?

Answer:
I don't know what your asking, if you mean a spin off from long-johns, yes, they resemble them, without the trap door of course, fire proof underwear is made of "Nomex", they prevent fire from reaching the skin for a short period of time, thus providing a margin of safety for those who wear them.
First answer by Rudiful2. Last edit by Rudiful2. Contributor trust: 1384 [recommend contributor recommended]. Question popularity: 1 [recommend question].