I recently returned from the Grand Canyon, where I hiked for a week and noticed that most of the otherwise well-equipped hikers were wearing synthetic clothing that wicked moisture away from their bodies–and that’s fine in humid climates and when it is cold, but in hot dry areas such as the Grand Canyon during spring, summer, and early fall, hikers should wear cotton clothing: the cotton absorbs sweat and keeps the moisture on your body, thereby cooling your body and slowing dehydration. All the desert survival books tell us to wear cotton during hot conditions in dry regions such as deserts.
But never wear cotton socks on hikes. Cotton socks hold on to the sweat from your feet, and wet feet lead to blisters and cracking. Wear merino wool socks, even in summer: the wool wicks the moisture away from your feet.
During cold weather (including cold days in the desert), wear synthetic or wool clothing that wicks your sweat away. Cold, wet clothing will rob you of body heat and lead to hypothermia.
Carry plenty of water and Nuun Hydration Tablets.