The plastic portion of a total knee replacement is made of high-density polyethylene. This is a material that has excellent wear and provides a good counter surface to the metal of the femoral component. Over the years, there have been several improvements to the medical grade polyethylene utilized. We have improved the way we sterilize the material and have learned to avoid the negative affects of radiation in the presence of oxygen. Over the last six years, the introduction of cross-linked polyethylene, which is a stronger material, has led to less wear in total hip replacement. Now, these types of cross-linked polyethylene are being introduced in knee replacement. We have seen the introduction of second-generation cross-linked polyethylene which seems to have advantages for fixed-bearing total knees. Whether or not these will solve all of the issues of wear in young active patients remains to be seen. More likely then not, a combination of factors including improved bearing surfaces on the metal side, improvements in polyethylene, and refinement of our implants including the use of mobile-bearing knees will all have a positive affect on the longevity of knee replacement. As manufacturers strive to improve the quality and durability of their implants, surgeons through a variety of techniques including use of computer-assisted surgery, are striving to improve the technique so longevity and function can be improved.