Swiss perc is hollow perc that typically resembles a disc with holes in it. Since the airflow does not have a direct path, it will split the smoke and water up between the holes increasing the surface area the smoke/vapor has to travel across. These made a cool functionality effect, and these percs were even the predecessors to fab eggs and exosphere styles of rigs
In the image below the smoke goes through small honeycomb perc, and then threw the Swiss Perc.
