Water naturallywets the pores of paper, causing the water to spontaneously wick into the paper.However, liquids do not wick into all porous materials.For example, pores in raincoats let heat pass from your body to the surroundings, yet water does not penetrate into the pores.The extent to which liquids pass through pores depends on their contact angle with the material (water on a waxed car has a high contact angle) and the surface tension of the liquid.Water, which has a large surface tension, will only pass through pores that it wets.Liquid metals have surface tensions that are nearly an order of magnitude larger than water and wet very few surfaces.As a result, they tend to assume a spherical shape and do not like to pass into porous surfaces.In fact,there is a technique calledporosimetry hat determines the pore size of a material by measuring the pressure required to physically force mercury—a common liquid metal—into pores that it otherwise would not naturally fill.