HEAT HOLDERS Women's 0.61 tog Microfleece Thermal Base Layer Long Sleeve Top Black 95% polyester, 5% elastane machine washable Heat Holders thermal microfleece base layer is a great choice for the ultimate thermal protection, perfect for wearing under your clothes for that extra warmth! Light-Weight - Our specially developed lightweight Microfleece has an excellent warmth to weight ratio making a highly versatile layer. Breathable Construction - Our light weight Microfleece construction is highly breathable allowing moisture to escape keeping you dry and warm throughout activity. Multi-directional Stretch - Our innovative knitting technology produces a multi-directional stretch for maximum freedom of movement. TOG rating - This has a massive TOG rating of 0.61, providing you with an extra layer of warmth. What is a TOG rating? It is a textiles way of measuring a piece of clothings thermal quality - the higher the TOG rating, the warmer the product will keep you!