The TVR was 200 deg inside during Le Mans this year... it's was pretty warm even in Istanbul in the rain! Seems like a sensible rule but a lot can be done by buying good breathable suits (the stretchy nomex) and refridgerating balaclavas... would've thought that was a better way of helping the drivers out without adding weight to the cars... look at the difference between Corvette and Aston at Le Mans: Corvette bought the good stretchy nomex suits, Aston insisted on free suits from a "suitable partner" (anyone who'd give them free kit)... the Corvette drivers were fine, the Aston boys had fire extinguishers emptied on them to try and keep them cool in the nice "shiny" suits they were wearing.
Some of the difference was down to the cars, but a huge amount is due to the kit:
Stand 21 have done some serious research on this with the French army:
http://www.stand21.fr/heatstress/heatstressc2c.htm
it's worth a read to understand why guys are fainting in cockpits and why most of the teams in the know at Le Mans race who are buying their kit rather than being given it are in the Stand 21 stretchy suits!
Cheers Rick
Yes I do wear their kit! And yes it's saved me a couple of times. But i'm not sponsored by them. The last guy who got free kit from them was Senna! If you're better than Senna than you might be eligible for a free set of gloves... but then I guess Rolex don't give away many watches either... unless u win Daytona!