Features of the Pearl Izumi Merino Thermal Wool Sock Transfer merino fabric combines wool and recycled polyester for sustainable Technical Performance 18.5-Micron fine merino wool Repreve recycled polyester created from recycled plastic water bottles Double weight knit for extra warmth Flat toe seam construction provides superior comfort over toes Anatomic arch compression for a Performance Fit Fabric Details Merino Wool/Recycled Polyester