From one of the best-known and widely-respected pipe companies, Peterson 9mm Pipe Filters are ideal for anyone who prefers a 9mm (European) filtered pipe. These are tubes of cardboard (with ventilated caps on either end) that are filled with fine granules of charcoal. The porous nature of charcoal allows it to absorb moisture readily, and its rough texture will grab onto and hold tars and particulates very well. Although it's up to the individual to determine how often to change the filters, we have customers who change each time, but most swap them out after more than four bowls. Keep you smokes nice and dry with Peterson 9mm Pipe Filters.