FLOSO Childrens Big Girls Winter Thermal Socks (Pack of 3) (2 Color Options) 100% Nylon Great quality kids thermal socks. Fiber: 90% Acrylic and 10% Nylon. Ideal for cold winter days or even on the ski slopes. Knitted with high bulk Acrylic yarn, giving the socks extra thermal warmth and a high tog rating. Girls and boys options available.