Why is ice so slippery?

In the past, the slipperiness of ice was explained by the formation of a liquid layer on the surface. According to this hypothesis, the heat caused by the friction force causes the ice on the surface to become liquefied and thus the material becomes slippery.

A group of researchers who wanted to understand why ice is extremely slippery first developed a device that can detect friction forces on the nanometer (one billionth of a meter) scale. Then, using this device, they examined how the structure of the ice changed due to friction forces. The results show that surface liquefaction has occurred in accordance with the description which is assumed to be correct in the past. However, the resulting thin film is much thinner than expected according to the theoretical predictions made in the past. Moreover, it does not seem possible that this layer, whose thickness varies from a few hundred nanometers to a micrometer, consists only of liquid water. Because the viscosity of the thin film (resistance of fluids to flow) is similar to that of oils rather than that of liquid water. Researchers suggest that the resulting thin film is a mixture of ice water and crushed ice. This structure is compared to the structure of the snow cone, one of the popular foods of summer days.

You can find the detailed information about the research published by Dr L. Canale et al. in Physical Review X.