The Patagonia R1 pants are made using Patagonia's Regulator R1* fabric. Highly breathable, moisture wicking* and compressible, they have a slim fit design that makes them ideally suited for use as a base or mid layer under a shell pant.Glossary:Regulator R1/R2/R3/R4:Insulating fabric that that conserves body heat, wicks moisture and is highly compressible. Available in 4 fabric weights, R1 is the lightest up to the heaviest R4.Wick/Wicking: The act of transferring moisture from the skin to the outer layer of a garment quickly and efficiently, where it evaporates. Provides a drier more comfortable environment inside a piece of clothing/equipment.