In this study, the potential of amphiphilic diblock copolymers on the example of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) and poly(4-methylstyrene)-b-poly(4-vinylpyridine) (P4mS-b-P4VP) for producing open-celled foams was evaluated. The porous foam structure was realised by employing carbon dioxide and water as environmental-friendly blowing agents. Rheological measurements in shear and elongation revealed a similar strain-softening behaviour of the diblock copolymers in the melt state. The transient shear and elongational viscosity of the P4mS homopolymer agreed with the linear viscoelastic prediction. On the contrary, the employed PS homopolymer showed strain-hardening. The rheological behaviour of the PS and P4mS homopolymers is consistent with their foaming ability. The PS homopolymer led to a homogeneous, closed cell structure, while the P4mS homopolymer did not foam at all. Because of strain-softening in melt elongation, the PS-b-P4VP diblock copolymer generated homogeneous, open-celled foams throughout the whole sample. In contrast, the P4mS-b-P4VP diblock copolymer generated partially open-celled structures in coexistence with compact areas. In this work, it was demonstrated that the combination of carbon dioxide and water led to open-celled diblock copolymer foams even if the major component of the block copolymer generates homogeneous closed-celled foams or is not foamable, respectively. (C) 2016 Elsevier Ltd. All rights reserved.