Ladies Heat Holders Welly Sock in a UK Size 4-8. Heat Holders are over 7x warmer than a basic cotton sock. They are made from advanced insulating yarn, our specially developed advanced fibres provide high performance insulation against cold with superior moisture wicking abilities. With long looped thermal pile, Innovative knitting technology produces our unique, extra long tooped cushion pile to hold in more warm air, increasing the thermal top rating. A soft Brushed Inner, Finally an intense brushing process maximises the amount of warm air held inside the sock for all day warmth and comfort.