Brand new 4 pack Merino Wool is a super strong natural fiber that's incredibly soft, will keep you warm in the winter and breezy-cool in the summer, and its natural moisture-wicking properties keep your feet dry and cozy. And that's just the fabric, before we add all of the sock tech features that come in every pair of Bombas. Features Seamless Toe Seamless Toe Stay-Up Technology Stay-Up Technology Cushioned Footbed Cushioned Footbed Honeycomb Arch Support Honeycomb Arch Support Y-Stitched Heel Y-Stitched Heel