I’d make one exception: cotton wants to hold water. Evaporative cooling needs water to evaporate. There are synthetic materials that will hold much less water, so they’ll weigh less from sweat and evaporate more quickly, providing a tiny bit more cooling. Plus many have protection from the sun reducing the amount of sunscreen that has to be worn.
There are a line of shirts known as “fishing shirts” that are made to be big, and they have vents to encourage air to circulate inside them. They work great.