Smartwool Men's Fritter Free Heel Slippers wool Sizing runs small - Men's US shoe sizes, recommend ordering one size up. Smartwool interior and exterior fabrics. Recycled Smartwool felt outsole, non-slip surface, recycled Smartwool felt footbed with EVA heel and arch support. For inside use only 60% Merino Wool, 40% polyester textile upper with manmade overlay. 80% Merino Wool, 20% nylon lining.