SUMMARY:The permeation rate of water in fully immersed, filled polymer films considerably exceeded that in films, of which one side adjoined water-saturated air or liquid water and the other dry air. This result may be explained by a preferential permeation in water-filled interspaces between the filler and the polymer matrix.In case of immersed alkyd resin films the permeation rate a t first increased with rising pigment concentration and then tended to decrease at higher concentrations. On the other hand with different water concentration adjoining both sides of the film, the permeation rate steadily decreased with rising pigment concentration. There is some evidence that under these conditions a dry boundary layer exists at the downstream side in which no interspaces may be formed a t the inner phase boundaries. This layer therefore acts as the main barrier against water permeation.