The kids' DOUBLE FACE SET The Double Face thermal underwear by is among the most universal pieces by Sensor. A special construction of the knit and the cut means that the T-shirt is reversible, with different thermal properties. The side marked as "plus" has a surface made of micropolyester silk, so it is suitable as an inner side in warmer conditions. The side marked as "minus" is made of micropolyester staple, which makes it perfect for colder temperatures. The difference in thermal resistance of both sides has been measured in laboratory conditions as 3.6°C.