Closed-cell polystyrene foam was utilized as a membrane buffer for separation of (bio)hydrogen. In the foam the cell walls form a structured complex of membranes. The cells serve as pressure containers of separated gases. The foam membrane can buffer the difference between the feed injection rate and the rate of consumption of the product. It can be utilized when biohydro.gen feeds a fuel cell and consumption of electricity is not synchronous with hydrogen production. The function of the foam was assessed using a cubic model and the theoretical data were checked experimentally by using gases present in the bioreactor (H-2, N-2 and CO2). It turned out that there is a considerable difference (hundreds of minutes) in time-lags of various gases in the polymeric foam, thus the foam is able to separate hydrogen and also to store it effectively. (c) 2007 Elsevier B.V. All rights reserved.