Exo-Terra BioDrain Terrarium Draining SubstrateExo Terra BioDrain Terrarium Draining Substrate is a natural, non decomposable substrate that facilitates healthy drainage in your reptile habitat, without decomposing like organic substrates. It also functions as a biological filtration system, allowing water to be recirculated for use in waterfalls and drippers. Natural non decomposable crushed lava substrate Creates a water drainage system Provides medium for biological filtration Ideal for