This story from Gizmodo helps explain why airsoft players need to avoid cotton fabric for cold and wet conditions. Even in warmer temperatures, wearing cotton will still be a problem even in the absence of rain as sweating heavily under cotton wear can also have a negative affect on you... "Cotton garments can absorb up to 27 times their weight in water, something which means they a) take forever to dry out and b) actively work to cool your body in even moderate temperatures.