Cotton is a highly absorbent material, and it gets heavier when wet. That is why it is important to season canvas tents to ensure they are waterproof. Cotton is not a good clothing option for rain because it is such an absorbent material, and it will cling to your skin, robbing your body of heat. If the cotton is waterproofed correctly, it can repel water more effectively, but it still won’t perform that well in the rain.