The invention relates to a foam for purifying and filtrating air, particularly filtrating toxic compounds, such as for instance tar and polycyclic aromatic hydrocarbons (PAHs) from tobacco smoke, and to a method to prepare this foam. The foam according to the invention is a foam comprising cavities and interstitial spaces situated outside of the cavities, the cavities being defined by walls, the walls of the cavities being composed of a crosslinked polymer and possible additives, the average largest dimension of the cavities being in the range of 30-350 νm, a considerable part of the cavities comprising two or more perforations in their walls, the perforations having an average diameter in the range of 5-300 νm, a considerable part of the perforations of adjacent cavities being positioned with respect to each other such that a continuous, non-linear path is formed, the foam having a porosity of at least 45 vol.% the porosity being defined as the volume percentage, based on the total volume of the foam, of that part of the foam accessible to matter passing through the foam, and the foam having a specific surface in the range of 0.1-15 m2/g.