The curing of 200 μm thick, surfactant-stabilized water-in-dicyclopentadiene high internal phase emulsion films by ring opening metathesis polymerization yielded 140–200 μm thick, open-cellular macroporous membranes with 81.5 ± 2% porosity. Depending on the support on which high internal phase emulsion (HIPEs) were cast, different polyHIPE membrane surface morphologies ranging from almost closed (on steel) to fully open (on glass) were obtained. At the same time, the interior morphology of the membranes was identical, featuring cavity and window diameters of 7 ± 5 and 1.4 ± 0.6 μm, respectively. The membranes were tough and ductile, as revealed by a Young's modulus of 125 ± 8 MPa and an ultimate strength at break, which occurred at 20 ± 2% elongation and 3.1 MPa. The swelling behavior of the membranes was tested in several solvents and finally the swollen membranes were functionalized by bromination, yielding still ductile membranes of 80.6 ± 1% porosity and bromide loading of 5 mmol g−1.