The investigation of the apparent diffusivity of water in thin layer iota-carrageenan-based films by FTIR-ATR spectroscopy clearly evidences the fundamental role of surface properties on water transfer. Water diffusivity in iota-carrageenan based biopolymer films ranges from 0.3 to 1.3 x 10(-10) m(2) s(-1) and is thus 10-100 times lower than that in highly hydrated carrageenan gels. The surface heterogeneity and composition when fat is added strongly influence the diffusivity by modifying the liquid water absorption at the inner surface. This study of diffusing molecules in liquid state is particularly interesting to mimic situations where direct liquid water contact occurs with the film, either liquid water itself or water from a highly hydrated matrix. In such cases, standard gas permeability measurements are inadequate, especially when film properties are modified by the diffusing molecules. (C) 2011 Elsevier B.V. All rights reserved.