Glide waxes enhance the speed of the gliding surface, and are applied by ironing them onto the ski and then polishing the ski bottom. Three classes of glide wax are available, depending on the level of desired performance with higher performance coming at higher cost. Hydrocarbon glide waxes, based on paraffin are common for recreational use. Race waxes comprise a combination of fluorinated hydrocarbon waxes and fluorocarbon overlays. Fluorocarbons decrease surface tension and surface area of the water between the ski and the snow, increasing speed and glide of the ski under specific conditions. Either combined with the wax or applied after in a spray, powder, or block form, fluorocarbons significantly improve the glide of the ski and are widely used in cross-country ski races.