A skate can glide over ice because there is a layer of ice molecules on the surface that are not as tightly bound as the molecules of the mass of ice beneath. These molecules are in a semiliquid state, providing lubrication. The molecules in this "quasi-fluid" or "water-like" layer are less mobile than liquid water, but are much more mobile than the molecules deeper in the ice. At about −157 °C (−250 °F) the slippery layer is one molecule thick; as the temperature increases the slippery layer becomes thicker.