Latex films have been produced through evaporation of aqueous dispersions containing polymeric particles. These films have a cellular structure : The cell cores are made of hydrophobic polymers, and the cell walls are made of carboxylic monomers that are copolymerized with the core polymers. The mechanical properties of these films are determined by the state of the cell walls. In humid environments, the cell walls take up water and lose their cohesive strength; consequently the films become brittle. The possibility of reinforcing the films through interdiffusion of core polymers across the cell walls was examined. Annealing the films at temperatures where these polymers are mobile produced extensive interdiffusion of low molar mass polymers across the cell walls. This had no effect on the mechanical properties of the films. Annealing at temperatures that caused fragmentation of cell walls produced interdiffusion of high molar mass polymers. At this stage the films became resistant to humidity.