This work presents a theoretical and experimental study on the specific migration process, describing the mass transfer of a model migrant Octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (I-1076), an antioxidant commonly used in the polyolefins processing. Film samples (LDPE), with initial concentration of Irganox between 1000 and 6000 (mg/kg), and thickness of 50-190 mu m, were placed in contact with fatty (EtOH 95%) and aqueous (EtOH 10%) food simulants at 40 degrees C for 20 days, in order to obtain the concentration evolution in the food simulant which was measured by HPLC. On the other hand, a phenomenological model based on a resistances-in-series approach was developed considering the diffusion through the polymer film, natural convection in the food simulant and the thermodynamic equilibrium between the polymer and the liquid simulant phase. For the thickest films, the diffusion coefficient of I-1076 through the polymer phase was estimated varying between 1.95.10(-13) (m(2) s(-1)) and 2.0-10(-13) (m(2) s(-1)) at 40 degrees C. On the contrary, the thinnest one shows a significant decrease of the diffusion coefficient value, which was evaluated in 1.0.10(-14) (m(2) s(-1)). This modification can be explained by means of a crystal distribution and size in the thinnest polymer film prepared by CAST extrusion. The mathematical model developed is a tool for prediction and analysis which can be used to facilitate the characterization of polymers, and it could predict the response as packaging for food in a specific application. (C) 2010 Elsevier Ltd. All rights reserved.