Smartwool teamed up with their athlete and ultrarunner Rob Krar to make a sock that can handle the longest trail runs. Introducing PhD® Pro Endurance Krar Print Crew. This running sock features Indestructawool™ technology for enhanced durability, our Virtually Seamless™ toe for added comfort, and our 4 Degree™ elite fit system for a dialed, performance-oriented fit—so you can stay confident on the most rugged trails. And body-mapped mesh zones keep things breathable mile 1 to mile 100. Get ready to rack up more miles than ever before.