All No Fly Zone socks are manufactured using yarns treated with permethrin insect repellent. Odorless and durable, permethrin repels common biting insects like mosquitoes, flies, chiggers, midges, ticks, and ants. And best of all, it doesnt alter the amazing qualities of our 100% US-made merino wool. Wearing the No Fly Zone Boulder lowers your chances of getting bothersome bites or worse, insect-borne diseases on your next day hike or backpacking trip.