Improved inspection techniques are described herein for identifying leaks in a plugged honeycomb body. The improved inspection techniques utilize a pore impediment and a test gas. The pore impediment is injected into the plugged honeycomb body, and the test gas is forced into the plugged honeycomb body. A thermal detector is used to collect thermal data from an inspection region of an outlet end of the plugged honeycomb body, and the thermal data is used to identify defects in the plugged honeycomb body.