The Sherpa Vayu Long Sleeve Crew is a merino wool blend with PrimaLoft Silver yarn to achieve a knit that allows the two components to work in tandem with amazing results. Wool content pulls moisture off the skin while PrimaLoft fibers push it through to the surface for faster evaporation. Primaloft fibers are water repellent so they do not create an environment that allows bacteria to grow in. This hybrid material dries faster, absorbs less moisture, is more durable, and regulates the body temperature better than wool can by itself. And all of this translates to an expanded level of comfort and safety for you when you're pursing your outdoor passions.