The Savinelli 9mm Balsa 733 Pipe Filters are designed for pipes that accept a 6mm filter. They resemble the "pith" of a reed on the outside. They are lightweight, porous, retain moisture, and all of this while preserving the taste and aroma of the tobacco in its true dimension. In other words, it is a piece of wood that may not retain as many harmful substances as activated charcoal, but the result will be the realistic performance of the essential oils in such a way that will impress you.