A matrix/puck/pineapple perc is a type of percolator used in a bong that’s main purpose is to filter and cool smoke prior to inhalation. A matrix perc is sometimes called a pineapple perc due to its design, a cylindrical shape with many horizontal and vertical slits. A percolator in dab rigs or bongs can also be made up of porous pucks that either lay flat or are curved. If curved, the perc can resemble a pineapple.
A matrix, puck, or pineapple perc diffuses a high volume of smoke as the smoke circulates in many different directions. A water bong is used to filter smoke over water, which can remove some smoke contaminants for a smoother hit, although a water hit can still be harsh. A percolator bong takes that filtration to the next level to cool and moisturize hits as it produces tiny bubbles as smoke passes through it. These tiny bubbles give more water surface for the smoke to contact as it filters away more contaminants in the smoke.