The absorption of air by a liquid foam was studied experimentally at various temperatures between 8 and 55 degrees C. It causes expansion of the foam and a gradient in cell size. The rate of expansion remains approximately constant following an initial transient. A theoretical analysis of the phenomenon is presented which assumes that the permeability of the liquid films to air is inversely proportional to their thickness and exponentially dependent on temperature. It is then possible to obtain experimental values of the permeability and of the activation energy for permeation which is similar to 85 kJ mol(-1). This is considerably larger than the activation energy for diffusion of air in pure water.