With all of the features that the PhD Run Ultra Light Micro offers, your newest technology may be in your sock drawer. Indestructawool technology provides you with enhanced durability, while a 4 Degree elite fit system makes for a performance oriented fit. And Shred Shield technology reduces wear and tear from your toes. It's breathable, comfortable, and built to help take you farther. Features: Indestructawool technology for enhanced durability 4 Degree elite fit system for a dialed, performance-oriented fit Shred Shield technology reduces wear from toes Body-mapped mesh zones for added breathability Virtually Seamless toe for enhanced comfort Achilles tab designed to prevent sock from slipping down into footwear Materials - 50% New Zealand Merino Wool, 45% Nylon, 5% Elastane Made in USA Smartwool Adult Sock Sizing Chart US Men’s Euro Small 3-5.5 34-37 Medium 6-8.5 38-41 Large 9-11.5 42-45 Extra Large 12-14.5 46-49