A component of a bong or dab rig that, when immersed in water, diffuses smoke to produce a smoother, cooler hit. Diffusers, which are typically a replacement for the downstem or attached to it, produce numerous smaller bubbles than a conventional downstem, increasing the surface area and cooling the smoke. Additionally, diffusers can reduce the volume of a bong or dab rig.

A bong or dab rig can function without diffusers, like percolators, but they improve the smoking experience.
A diffuser makes more bubbles by breaking up smoke before it hits water in the main chamber of a bong or dab rig. Because of this increase in surface area, the water can perform better as a cooling agent.By reducing coughing and throat burn, diffusers can enhance the enjoyment of smoking or dabbing.
A bong or dab rig may also sound quieter due to smaller bubbles.Small bubbles produced by a diffuser sound more like a gentle roll that can go unnoticed, which is great for discretion because large bubbles make a lot of noise and are often described as a chugging sound.

If a diffuser is not included with a bong or dab rig, it usually can replace removable downstems but not fixed downstems. You can usually swap out the diffuser by finding one that fits the downstem in the same way. After that, use the bong or dab rig as usual. A diffuser simply enhances the experience rather than altering how a bong or dab rig is used.