Abstract: The invention relates to a transparent polyurethane foam wall optionally containing microorganisms, and a process for the preparation thereof, and the use of this wall in a biophotoreactor. This wall has pores, in which are distributed microorganisms and the pores are closed on one of the faces of the wall, in such a way that said face is impermeable to liquids and gases, while the other face of the wall has an open porosity. Thus, by circulating a liquid nutrient medium and a gas along the second face of the wall and exposing the first face thereof to light, it is possible to culture microorganisms and collect the metabolites formed by them in the liquid medium.