The U.S. Marine Corps has banned it troops from wearing high tech underwear, because of fire hazard. This stuff melts when exposed to very high heat, say from an explosion. Many soldiers and marines saw this coming, as fire departments also tend to forbid the use of these items. The word got around about the fire risk, because many reserve troops are firemen, and know of the dangers.
The expensive "high performance" underwear was originally created for athletes and outdoors enthusiasts. This clothing handles heat and sweat much more efficiently than your standard cotton undergarments. In Iraq's sweltering climate, these items have been every popular, even though they are expensive.
This "athletic underwear" is made out of synthetic material, including nylon, acrylic and polyester. It melts when exposed to flame. However, very few troops get injured, and fewer still have the kinds of injuries that would lead to the synthetic materials melting. But all troops out on combat missions during the Summer are at risk of heat related injuries. There have been thousands of those, some of them quite serious. Commanders will be under a lot of pressure from the troops, to look the other way as everyone tries to avoid heat stroke by wearing the forbidden underwear.