Many additives are commercially used to add more favorable qualities to films. The bleeding process by which the additive in a film comes to the surface is considered. A new bleeding model of additives in a polypropylene film under atmospheric pressure was investigated. Solubility and diffusion are found to be important for explaining this bleeding process. It was found that the experimental results were explained more precisely by assuming a two-step transport process between the crystalline regions and the amorphous ones. The solubilities and diffusion coefficients of UV-stabilizers such as 2-(2H-benzotriazol-2-yl)-4(1,1,3,3-tetramethylbutyl)phenol and 2-(2H-benzotriazol-2yl)-4-inethylphenol were determined at 40 degrees C. The difference between the saturation solubilities and the diffusion coefficients of UV-stabilizers was discussed by comparing with the results of molecular dynamics (MD) simulation. (9 2007 Wiley Periodicals, Inc.