Honeycomb ceramic substrates, honeycomb extrusion dies, and methods of making honeycomb ceramic substrates

A method of making a honeycomb ceramic substrate, comprising:

• extruding a ceramic or ceramic-forming batch material through a honeycomb extrusion die to form green honeycomb substrate including a lattice of intersecting walls defining a honeycomb network of flow channels extending between an inlet end and an outlet end of the green honeycomb substrate, wherein each flow channel is defined by a plurality of channel walls of the intersecting walls with at least two of the plurality of channel walls including concave inner surfaces facing a center of the corresponding flow channel from central portions of the concave inner surfaces to concave corner portions facing the center of the corresponding flow channel, the concave corner portions being where each of the plurality of channel walls intersects with another one of the plurality of channel walls;
• drying the green honeycomb substrate;
• and
• firing the green honeycomb substrate into the honeycomb ceramic substrate.