The Farm To Feet Boulder No Fly Zone sock is manufactured using yarns treated with permethrin insect repellent. The odorless and durable, permethrin repels common biting insects like mosquitoes, flies, chiggers, midges, ticks, and ants. It features the amazing qualities of their 100% US-made merino wool. The sock features outer nylon plaiting, full-density cushioning, seamless toe closure, comfort compression and is durability assured. It consists of 72% US Merino Wool, 26% US Nylon and 2% US LYCRA® Spandex. The medium is women's 7 to 9.5 and large is men's 9 to 11.5 and the XL is for sizes 12 to 14.