For solid lubricant films such as oxides, soft metals and molybdenum disulfide in a resin low friction and low wear have been found when the film thickness lies between 10−6and 10−2cm, and high friction and high wear outside these limits. At the 10−3−cm limit, the rise in friction occurs because the load is carried by the film rather than by the substrate, while the rise in wear is caused by the formation of large wear particles. The experimental data appear to agree reasonably well with theoretical predictions based on the concepts of characteristic junction size and wear particle size.Presented as an American Society of Lubrication Engineers paper at the Lubrication Conference held in Minneapolis, Minnesota, October 18–20, 1966.