Norrona Senja Merino Lightweight Short Socks Caviar Black 37-39 5816-23 7718 37-39. Was used a combination of Merino wool polyamide and elastane because this creates the best socks for trail running. The wool because of its temperature regulation natural order-resistant properties and its ability to absorb moisture in a good way. The polyamide for its strength quick dry and low friction. The elastane for the ability to create stretch but we want to use as little as possible because of elastanes moisture take up. The 215 micron merino wool is GOTS certified. Extra cushioning at the bottom of your feet for increased protection. The arch of the product has been outfitted with a snug premium Merino Wool band that will keep them in place. And both the heel and the toe of the socks have been reinforced for maximum defense against typical sock holes. The fit is technical. Package Contents: Norrona Senja Merino Lightweight Short Socks Norrona 5816-23 7718 43-45: Senja Merino Lightweight Short Socks Caviar Black 43-45 Norrona 5816-23 7718 40-42: Senja Merino Lightweight Short Socks Caviar Black 40-42 Norrona 5816-23 7718 37-39: Senja Merino Lightweight Short Socks Caviar Black 37-39 Norrona 5816-23 7718 37-39: Senja Merino Lightweight Short Socks Caviar Black 37-39