Perlite is a incredibly light porous volcanic material that has been popped like popcorn under high temperatures. Having a huge surface area with millions of microscopic cell it is able to hold large volumes of water, this water easily evaporates to increase relative humidity in a fruiting container such as a "mono tub" or "SGFC (Shotgun Fruiting Chamber)" .


A mono tub and SGFC are a simple container with holes drilled for air exchange, perlite is soaked in water to holding capacity, drained and put in the bottom of the tub where it will let the water evaporate over time and increase the humidity within the chamber.


Instructions to build your own fruiting chambers:


Perlite - Humidity Buffer