In this paper, a new method to obtain the effective diffusion coefficient of the gas contained in closed cell foams under static loading is presented. Compressive creep experiments were performed on six low-density polyethylene (LDPE) and two polyethylene-co-vinyl acetate (EVA) foams of different densities using a home-designed compressive creep apparatus. The modelling of the evolution of pressure inside the cells was performed using an isothermal compression model. The effective diffusion coefficients were obtained from pressure decrease with time using an analytical solution of the diffusion equation. The values obtained agreed with those in literature and were dependent on both foam density and chemical composition. (c) 2005 Elsevier Ltd. All rights reserved.