A porous substrate and method of forming a porous substrate including providing a fiber material, providing at least one extrusion aid, and providing at least one washcoat precursor. The fiber material, the at least one extrusion aid and the at least one washcoat precursor are mixed to provide an extrudable batch. The extrudable batch is extruded into a green substrate. The green substrate is fired to form a porous rigid substrate and to form a washcoat at least partially coating the fiber material.