The manifold possibilities to apply coatings made from biopolymers require the design of such membranes with functional properties. The influence of different additives and process parameters on the mechanical stability and penetrability of biopolymer membranes, especially of films based on alginates, is given in this work. Spheres of alginates made by the falling droplet method were used as model system. Besides different effects of additives it turned out that the mechanical stability and the penetrability could be influenced independently.