Perlite is a lightweight, porous substance and is recognisable as little white rocks. It is a type of volcanic glass that expands when heated, and is a popular choice as a hydroponic grow medium due to it’s ease of use. Perlite offers great water retention and drainage while providing good aeration for healthy root development. Perlite has a natural pH level of around 7.0. Perlite will not decompose, and can be washed and reused. It is frequently used as a combination with other grow media such as Vermiculite.