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.