Running in bad socks sucks. You can drop hundreds of bucks on the best running shoes, but if you stick your foot into an old gym sock, you still risk ending up with blisters. Running socks—along with running underwear—are probably as mission-critical to your comfort as anything else you work out in. If your socks fit poorly, hold onto sweat, or fail to cushion your steps, it’s a fast ticket to hot spots and Blisterville. Check out the rest of our outdoor guides, including the Best Rain Jackets and the Best Sunscreen.