The rule book stats that any three layer suit or any suit with a SFI 3-2A/5 rating or higher, does not require the use of underwear. A buddy of mine is looking at buying a Simpson STD.19, two layer, one piece suit that claims a rating of "SFI 5". So can anyone tell me if that SFI 5 rating is considered a higher rating than the SFI 3-2A/5? Basically, would it be legal to use without underwear underneath? Thanks for the help!