For acrylic painting. Will keep acrylic paints moist and workable for weeks. Clear lidded plastic tray contains three sheets of reservoir paper and 12 sheets of semi-permeable membrane paper. Stay-Wet works by osmosis. Moisture evaporating from the surface is replaced by water from the dampened reservoir paper beneath the semi-permeable membrane which forms the working surface of the Stay Wet Palette. The acrylic paint does not travel across the membrane, so stays on the top of the membrane paper.