This investigation seeks to establish the effect of pretensioning and solvent vapor treatment on polypropylene films. There are observed changes in the thickness of the polypropylene films. It is surmised that relatively small molecules such as chloroform, petroleum ether, dichloromethane, and toluene diffused into the polymer film more easily and resulted in maximum percent elongation in the shortest possible time. Decalin and tetralin, which are good solvents for polypropylene, brought about low percent elongation value at 27 degrees C and their behavior is explained in terms of the high boiling point of the liquid and their ability to contribute low vapor pressure on the polypropylene film at the temperature of investigation. Attempts to relate the absolute difference between the solubility parameter of the polymer and the various solvents, Delta delta, with the mechanical properties of the polypropylene film showed complex relationships. However, chloroform and reformate with Delta delta = 0.2 MPa(1/2) are most soluble, whereas naphtha and petroleum spirit with Delta delta = 1.7 MPa(1/2) are least soluble for the pretensioned polypropylene films.