Mares Ultra-Stretch 5mm Flex Sock Mares Ultra-Stretch 5mm Flex Sock Durable Nylon I Neoprene Rubber Open Cell Neoprene Foam Interior Glued & Flat-Lock Stitched Seams for Strength and Added Durability Great for Use with Snorkeling and Free-Diving Fins Wear Under Dive Boots for Added Warmth in Cold Water Great with Water Sandals, Shoes for Rafting, Canoeing, Kayaking, Mountain Biking Any Active Sport where Feet Need-to-Stay-Warm while Wet