There are two types of catalytic converters that are commonly used in cars: 1) Monolithic Converter and 2) Ceramic Converter.
Monolithic converter is made of a single piece of ceramic material that contains channels or honeycombs. The exhaust gases flow through the channels and the catalyst coats the surfaces of the channels. This type of converter is more efficient because the gases have to travel a shorter distance.
Ceramic converter, on the other hand, is made up of many small pieces of ceramic materials (called cubes) that are stacked together. There are gaps in between these cubes and the exhaust gases have to travel through these gaps. This type of converter is less efficient than monolithic converter but it can withstand higher temperatures.