In this paper a mathematical model for prediction of moisture gain over storage time for binary mixtures of moisture sensitive products was developed, which considered both the moisture transfer through the polymeric film to the headspace and from the headspace to the product. Moisture content within the product was assumed to be uniform for a given time and to relate to the headspace humidity by the GAB sorption isotherm. The transient period of these experiments was used to estimate the mass transfer coefficients. The model was validated by monitoring the moisture take up by breakfast cereal and chocolate powder mixture in different materials, oriented polypropylene (OPP) and low density polythelene (LDPE), during storage at 25°C and 75% relative humidity (RH). The model showed that for mixes some bias was clear, particularly for the cereal, probably owing to interactions between the products. If the resistance of the product to moisture uptake were not taken into consideration, the model would over-predict the experimental results by up to 20%.