I recently ran a relay trail race with some friends and ended up with very bad blisters. They recommended swiftwick socks, so I order a couple pairs. After I placed the order, they told me that I should have ordered one size larger than the sizing chart indicated. When the socks arrived, they did feel too tight. I reached out to customer support via e-mail and 2 pairs of larger size were immediately dispatched to me at no charge! What great customer service! I've already run in them a couple times and no blisters! Thanks so much!! -- Swiftwick customer for life