ProRep Drainage Medium is produced by firing ash at a high temperature. As it fires the air bubbles in the material expand to form a honeycomb of interconnected chambers and create an inert, hard and lightweight material that will hold moisture and provides a large surface area for the growth of beneficial bacteria. Used in the base of bio-active terrariums it creates a reservoir of water which moistens the substrate from below and helps to create a natural moisture gradient. The large surface area within each ball provides the ideal habitat for beneficial bacteria which will neutralise potentially harmful waste products formed within the ecosystem.