Smartwool Women's PhD&uml; Outdoor Medium Pattern Crew Other Indestructawool utilizes a proprietary yarn and construction method which strategically places Merino and reinforcement fibers where they are needed most. The result is the most durable and comfortable wool sock ever made. 4 Degree elite fit system uses two elastics for greater stretch and recovery. Narrower profile provides perfect women's-specific fit Ventilation designed for end use: more mesh in Ultra Light and Light weights ensures maximum breathability, thermoregulation, and moisture management.