Fins

Fins: When added to a suit of armor, these thin metal projections allow your body to radiate heat more efficiently. While wearing a suit of armor fitted with fins, you take only a –2 penalty on Fortitude saves against damage dealt by hot environments and on Constitution checks to avoid heatstroke, instead of the usual –4.

Armor Extra
Cost: +50 gp
Weight: +2 lb

Source: Sandstorm