Originally Posted by PeteHski

Sweat wicking is by far and away my number one priority in cycling gear and cotton is the very last thing on earth I would wear on the bike for that reason alone. I love cotton OFF the bike, but not a chance I'd go out for a hard ride with a cotton T-shirt. Might as well just throw it in a bucket of water before putting it on.

Merino wool is pretty good though and has the advantage of not stinking when sweaty. But the really thin summer Merino tends to disintegrate after a few washes, so I only use mid-weight Merino for Spring/Autumn rides.