Wool Can Be Cool: Water‐Actuating Woolen Knitwear for Both Hot and Cold

Abstract As a second skin of the human body, clothing offers protection and aesthetic qualities. Because of the inability of materials to adapt to different weather conditions, different clothing is required for different seasons, namely, thin and open garments for summer, thick and closed ones for winter. Moreover, the body maintains its internal core temperature (37 °C) through sweating and shivering. Herein it is reported that woolen knitwear can provide not only warmth, but also a cooling sensation when a body sweats. The fascinating water‐responsive switching (opening/closing) of the knit pores keeps the skin dry, thus helping to maintain a constant body temperature, providing comfort and safety.