Many times at Swix we are asked what our BD waxes are, and when to use them. The following article adapted from a paper written by the two top Swix Chemists in Norway should help to answer some of those questions.
When gliding on clean, fresh snow, two of the important properties of ski wax are 1: to create a hydrophobic surface repelling water, and 2: create a surface that adapts the hardness of the ski base to the underlying snow. When gliding on snow that is contaminated by dirt or other foreign particulates, a third element is introduced. This element has different properties than clean, fresh snow and increases friction between the ski base and the snow. Therefore the properties of glide wax working on clean snow need to be supplemented by a third one, that adapts to the contamination and increased friction. When gliding on particulate contaminants occurs, the probability of dry type friction is increased. Since contacts of the dry friction contribute most to the total friction, it is important to find a way to lubricate these areas. Solid lubricants are especially suited for dry friction reduction.
The idea behind solid lubricants is that the lubricant has large compression strength but low shear strength. Why is this important? A high compression strength aids in separating the two gliding elements (the ski base and the snow), and the low shear strengths lower the total energy needed to move the ski base over the snow which causes a reduction in friction. Common solid lubricants such as: graphite, molybdenum disulfide, and boron nitride show these characteristics. An analogy to such materials is a deck of cards. The cards can take considerable pressure when a downward pressure is applied but they slide when a transverse (sideways) force is applied.
Swix developed the BD waxes (that contain solid lubricants) leading up to the 2002 Olympic games. This development came in response to the largely man-made snow conditions at Soldier Hollow. Since then, these waxes have proven to work well over a range of conditions that increase friction and thus require an additional lubricating substance other than normal ski wax. These conditions include: dirty snow, abrasive (and dirty) manmade snow and older or cold dry snow. Though cold dry snow is not dirty, the lubricating liquid water layer is poorly developed. This means that the snow is hard and not as slippery which gives higher friction. Therefore, under such circumstances as described above it is necessary to use waxes with a solid lubricant as an additive.