Method for producing a filter

A method for producing a filter for purifying exhaust gases discharged from an internal combustion engine of an automobile or the like, comprising the steps of:

• preparing at least two kinds of foamed bodies made of an organic compound;
• said foamed bodies having different cell densities from each other and being provided with pores communicated with one another respectively;
• assembling said at least two kinds of foamed bodies into a columnar composite body so that said foamed body having highest cell density is positioned in the outer peripheral portion of said columnar composite body;
• immersing said composite body into a ceramic slurry bath for attaching said ceramic slurry to said composite body;
• removing said composite body from the bath with ceramic slurry attached thereto;
• drying said composite body to which said ceramic slurry is attached;
• repeating said immersing and said drying steps until the pores of said foamed-body positioned in the outer peripheral portion are substantially clogged with said ceramic slurry while the permeability of said foamed body positioned in the central portion is maintained;
• and
• firing said composite body to which said ceramic slurry is attached to burn off said organic compound and sinter said ceramic slurry;
• whereby a filter is obtained for purifying exhaust gases, which is composed of a reinforcing wall and a gas-permeable portion and has a unitary structure of partially different apparent densities.