The Patagonia Back Step Shirt is built from a hemp and organic cotton plain weave. Hemp fiber is naturally more breathable than cotton alone and breaks in quickly without losing its structure, so the shirt wears lighter and airier from the first day and keeps improving with use. What Our Gearhead(R) Experts Are Saying:"The plain-weave hemp-cotton fabric breathes more openly than a standard cotton shirt, so it stays cool against the skin on warm days without feeling stiff or scratchy."