Diffusion is used to cool and purify smoke when smoking cannabis. Diffusion is usually achieved in a bong (or water pipe) through the use of a percolator or a diffuser, which causes the smoke to spread out (diffuse) in the water.
“My bong has 300-hole percolator, the diffusion is insane!”
“The diffuser makes the bong purr instead of glug.”
What is diffusion?
Diffusion is the movement of smoke, vapor, molecules, atoms, etc. from an area where it is highly concentrated to an area of low concentration. For example, milk mixing into coffee diffuses the coffee—similarly, cannabis smoke mingling with water in a bong is diffused by the water.
Diffusion cools and purifies smoke by increasing the surface area of the smoke exposed to water. Thousands of smoke bubbles have much more surface area than one big smoke bubble.
Cooled, purified smoke can be inhaled in greater amounts than hot, ashy smoke, so a diffuser can enable larger inhalations and potentially higher doses of THC. However, water purification with diffusion not only reduces temperature and ash volume, but THC content as well—a bong with a nice diffuser might not get you higher, but it certainly feels more gentle on the throat.