SmartWool Women's PhD Run Ultra Light No Show Socks 51% Merino Wool, 45% Nylon, 4% Elastane Made in USA Ultra Light Cushion: Minimal cushioning for maximum next-to-foot performance without added bulk. PhD = Built for Performance in the Highest Degree. 4 Degree Elite Fit System: Uses two elastics for greater stretch and recovery to keep the sock in place. ReliaWool: Patented ReliaWool technology in high impact areas provides superior durability. Women's-specific mesh ventilation zones provide additional breathability and moisture management - Narrower profile provides perfect women's-specific run fit. Virtually seamless toe - Sock Height: Hidden - Lowest profile run sock available. 200 needle construction provides highest knit density while maintaining ultra light weight. Style: SW0SW185