Our Ultralight Gear line is our lightest line yet. 34% Bison fiber, 33% Merino and 33% Bamboo. Sometimes a product idea just completely makes sense. We spent a lot of time experimenting and futzing with the base yarn for our B.O.S.S. Socks, trying to get something extremely lightweight, breathable, wicking, cushioning and durable. Getting the proper ratios of bison, wool, bamboo, to insulate, breathe and wick.. and the right amount of twist, not so tight it doesn't have "spring" not so lofty it doesn't wear properly. This line will do the job of keeping you warm without weighing you down.