Well, maybe not that extreme. However, after reading this article in the July 2013 edition of SportsCar, I found that there are inherit risks in wearing cotton t-shirts and especially Under Armour type shirts under the suit.
It states that, “Wearing (standard clothes) under the race suit carries the risk of internal combustion next to the skin; while the race suit does not burn, you can trap the burning and heat buildup against the skin.”
It is perfectly legal to wear whatever you want under your suit, provided that the suit passes SFI or FIA certification to be a stand alone garment for fire protection. But, legal doesn’t always mean safe.
Not to mention, many products that stretch and wick sweat like the Under Armour (which I love btw) are made of synthetic fibers called acrylics (a kind of plastic). The perform extremely well in high heat activities. But, when burned they melt and drip. What that means to us race car drivers is that a material like this has to be surgically removed from the skin if it is melted on the skin. Not an ideal scenario.
While it may not be suicidal, there are better ways to protect ourselves and be cooler under our suits. Further, all FR isn’t created equal. More to follow.