To understand the water vapor transport through a polypropylene film at near ambient temperature, water vapor permeation and sorption measurements were carried out using tritiated water as tracer. The activation energy and frequency factor of the permeability were found to be 11 kJ/mol and 1.5 x 10-10 cm3(STP) cm cm-2 s-1 Pa-1, respectively. The corresponding values of the solubility were determined to be -30 kJ/mol and 2.9 x 10-10 cm3(STP) cm-3 Pa-1. Because the permeation can be described by a one-dimensional diffusion model, the diffusion coefficient was evaluated from the quotient of permeability and solubility. The activation energy of water diffusion through polypropylene was calculated to be 41 kJ/mol.