In this work, the diffusivity of three different migrants is investigated in water plasticized polyamides, while changing humidity at a steady temperature, and also in dry polyamides tested at different temperatures close to the glass transition point (Tg). The effect of hydration on the structure and the barrier properties of polyamides are investigated and the results reveal that the diffusion coefficient (D) can be described by a single Williams-Landel-Ferry type equation, expressing D as a function of the (T - Tg) parameter. This correlation is found valid regardless the cause of (T - Tg) variation that could be temperature increase or Tg reduction due to water induced plasticization. At the same time, the effect of specific interactions between the polyamidic matrix and the diffusing molecules is also investigated, indicating that such interactions are capable of delaying the diffusion process regardless the temperature increase or the extent of plasticization. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012