Abstract: A method for making multi-channel structures suitable for use as filters, catalyst carriers or the like.A composite rod comprising an outer shell and an inner core is formed of respective mixtures of powders. The mixture for the outer shell comprises a sinterable powdered structural material such as ceramics, metals, intermetallics, and a powdered binder such as paraffin, wax or polymer. The inner core comprises a powdered channel-forming filler material such as melamine or polymers, or soluble inorganic compounds or a metal that can differentially be removed from the structural material of the shell.The composite rod may be deformed, as by extrusion, to reduce its diameter. In any event, a bundle of composite rods is assembled and deformed, as by extrusion, to reduce the diameter of the bundle and of its component composite rods.