An implant layer serving as a sliding surface for a second (eg metal or ceramic) part of a human joint prosthesis comprises 60-99 wt.% of a base polymer with the remainder being of one or more finely-divided fillers which (i) are of very small size with breadth : height : length ratio 1 : 1 : 1 - 1 : 4 : 400; and (ii) are such as to influence at least one of the following properties : abrasion reduction; cold-flow reduction; lubrication improvement; strength increase; age cracking reduction; or increase in wetting of the composite.
