As any armed forces member who's served in the Middle East can tell you, it's ludicrously hot even without the additional 20kg+ of clothing and armour. That's why the DoD is offering cash money to anyone that can fabricate some "Thermally Responsive Fibres".
Specifically, the DoD wants "Thermally Responsive Fibres for Environmentally Adaptive Textiles" (don't worry if you aren't sure what those are — they haven't been invented yet). These are fibres that adapt the amount of insulation they provide dependent on both the external and body temperatures. Essentially, it's got to be cool when you're hot and warm when you're cold. What's more, garments fabricated from them have to be hypoalergenic, be sturdy enough to survive 500+ temerature cycles, a three-month mission, and 20 wash cycles. [US Army via DVice]