Collections Etc Natural Stone Room Humidifiers - Set Of 2 Pair of room humidifiers naturally restore moisture into the dry air in your home. Simply fill the black ceramic bowls with water, and the white porous clay balls will release moisture into the air through natural evaporation. Significantly improves the air quality in your home, especially during dry winter months. No electricity required. Large measures 4 1/2" Dia., Small 3 1/2" Dia.