We teamed up with Smartwool athlete and ultrarunner Rob Krar to make a sock that can handle the longest trail runs. Introducing our 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.