I was told to wear Nomex long underware and a single layer suit because it was cooler than a two layer in the hot weather. It gives you an air pocket between the layers also. Most people seem to wear a regular t-shirt under the racing suit which has no fire protection. You can wash the underware after each race and not wash the suit everytime helping to extend its life. I have been happy with this arrangement. Since this is the only thing I have worn I can not compare it to the alternative.