lubricating layer of water, caused by the heat of friction between the ski and the snow in its passing. Colbeck suggests that the optimum water film thickness is in the range between 4 and 12 μm. However, the heat generated by friction can be lost by conduction to a cold ski, thereby diminishing the production of the melt layer. At the other extreme, when the snow is wet and warm, heat generation creates a thicker film that can create increased capillary drag on the ski bottom. Kuzmin and Fuss suggest that the most favorable combination of ski base material properties to minimize ski sliding friction on snow include: increased hardness and lowered thermal conductivity of the base material to promote meltwater generation for lubrication, wear resistance in cold snow, and hydrophobicity to minimize capillary suction. These attributes are readily achievable with a PTFE base, which diminishes the value added by glide waxes. Lintzén reports that factors other than wax are much more important in reducing friction on cross-country skate skis—the curvature of the ski and snow conditions. Glide wax Glide wax can be applied to alpine skis, snowboards, skate skis, classic skis, back-country skis, and touring skis. Traditional waxes comprise solid hydrocarbons. High-performance "fluorocarbon" waxes also contain fluorine, which substitutes some fraction of the hydrogen atoms in the hydrocarbons with fluorine atoms to achieve lower coefficients of friction and higher water repellency than the pure hydrocarbon wax can achieve. Wax is adjusted for hardness to minimize sliding friction as a function of snow properties, which include the effects of: Age: Reflects the metamorphosis of snow crystals that are sharp and well-defined, when new, but with aging become broken or truncated with wind action or rounded into ice granules with freeze-thaw, all of which affects a ski's coefficient of friction. Moisture content: The percentage of mass that is liquid water and may create suction friction with the base of the ski as it slides. Temperature: Affects the ease with which sliding friction can melt snow crystals at the interface between ski and snow. Properties A variety of glide waxes are tailored for specific temperature ranges and other snow properties with varying wax hardness and other properties that address repellence of moisture and dirt. The hardness of the glide wax affects the melting of the snow to lubricate its passage over the surface and its ability to avoid suction from meltwater in