Definition - What does Diffuser mean?
A diffuser is a special type of modified downstem used on a bong, bubbler, or water pipe. It looks similar to a glass test tube but is a tube that is sealed on one end and on the other end has a small number of open slits.
The slits of the diffuser break up the smoke so it makes smaller bubbles and is cooled even further by the bong water. The cooling effect makes for a smoother hit that is easier on the inhaler's throat and lungs.
Hydrolife explains Diffuser
Diffusers are often used by medical marijuana users who have pulmonary issues because the smoother hit reduces coughing and helps alleviate any burning in the throat caused by the cannabis product’s smoke.
A diffuser sits at the bottom of the bong. The slotted end is slightly submerged in the bong water. The slits create small bubbles which have greater surface area than large bubbles that are typically produced by a normal downstem that has only one large opening in the end. The diffuser’s small slots allow the water to filter the smoke more efficiently.
The smaller bubbles also make the bong virtually silent, unlike bongs with normal downstems, which can be heard bubbling every time a user takes a hit from the burning cannabis.
Diffusers are manufactured by a large number of companies. Most downstems on a bong can be easily pulled out and replaced with a diffuser.