A very thick wool blend sock lined with terry throughout. The long terry loops inside the sock trap air next to the foot making an insulating layer, which keeps warm air in and cold air out. The density of these terry stiches is what makes the Thermal Sock so effective. Reinforced heels and toes for extra strength and durability. An ideal wool work sock for those working in cool rooms or cold conditions but also a great thick sock for outdoor activities like hiking, camping and 4WD expeditions.