A process for producing a porous ceramic filter for use in the filtering of particulates from diesel exhaust gases, and the filter so produced, in which a foamable ceramic composition based upon an aluminosilicate hydrogel binder is expanded into a self-supporting, open-celled porous body of desired shape by virtue of in situ reaction between components of the composition, and thereafter treated to substantially reduce its alkali metal content and fired to produce ceramic bonds, the process further preferably providing on the intended outlet surface of the filter a thin porous ceramic membrane layer whose pores have an average diameter less than that of the pores within and at other surfaces of the ceramic filter.