The thermal foot cover is an article of footwear to be worn when the wearer's foot is subjected to cold temperatures. The thermal foot cover has an upper cover portion attached to a bottom panel to define a cavity for insertion of a wearer's shoe-encased or boot-encased foot or a wearer's foot. The upper cover portion and the bottom panel are made from a material comprising an outer covering, a radiant barrier and a inner covering where the radiant barrier is sandwiched between the outer cover and the inner cover. The radiant barrier is the insulation system of the thermal foot cover, which reflects the wearer's body heat back inside the footwear and keeps the wearer's feet warm. The thermal foot cover is flexible, lightweight and readily washable due to the use of the radiant barrier as the insulation system. The addition of a cavity enlargement means and a means for fastening the cavity enlargement means can be used to facilitate the insertion of the wearer's shoe-encased or boot-encased foot or the wearer's foot into the thermal foot cover and facilitate securing of the thermal foot cover to the wearer's shoe-encased or boot-encased foot or the wearer's foot and ankle to prevent loss of body heat when the thermal foot cover is being worn. A coating may be added to bottom of the thermal foot cover to provide a non-skid surface for walking. A flexible sole may also be provided for increased durability.