HOCOSA Kids’ / Children’s Long-sleeve undershirt made out of precious natural silk and organic merino wool. Certified organic silk wool includes 30% natural silk and 70% organic merino wool and combines the best of both materials: silk’s smoothness and wool’s warmth. Silk wool underwear is always comfortable to wear, with the wonderful warmth of wool and the sweet softness of silk. Soft merino wool and clean natural silk are a good combination for both summer and winter. In the winter silk wool is a wonderfully soft undergarment, and in the summer it can be worn on its own. Care Instructions.