Armorbright

Armorbright: This metallic paint is applied with a brush to the outside of a suit of armor (requiring 1 minute to apply), producing a shiny surface that reflects the light of the sun to reduce the effects of hot weather on the wearer. For 24 hours after applying armorbright to a suit of armor, you gain a +2 bonus on Fortitude saving throws to avoid heat dangers. Armorbright also raises your level of protection against heat by one step (see page 14). Armorbright is not effective in hot environments with no sun, such as the Elemental Plane of Fire.

Cost: 50 gp per flask
Weight: 1lb.
Craft (Alchemy) DC 25

Source: Sandstorm