The boundary film forming properties of polymeric viscosity index improvers are examined in an elastohydrodynamic (EHD) contact. Ultrathin interferometry is used, a recent development of conventional optical. interferometry, which allows the film thickness generated in a point contact to be measured down to a value of 1 nm. The ability of polymers to adsorb on the solid/liquid interface is shown to depend strongly on the polymer type, those without a polar group showing little or no boundary film forming properties, while those with a polar group are able to generate a boundary film of approximately 20 nm. These boundary films appear to be viscous sublayers with a viscosity up to 30 times higher than that of the solvent base stock, At very slow speeds, this enhanced viscosity layer generates an EHD type film many times that of the bulk fluid. In the higher temperature ranges studied, this adsorbed layer is observed to eventually fall off to the lowest measurable value of 1 nm.