Merino yarn is a natural fiber pleasant to the touch but also performing when it comes to ride. It is naturally antibacterial and works for all seasons: it keeps you warm and dry when it's cold and cool when temperature raises. They have terry-cloth inserts on underfoot to keep your feet dry and comfy and an elastic arch-brace for a more anatomic fit. Note: Merino Socks have slightly bigger sizes because they tend to loose 5 / 7% of the fit after the first wash.