Galapagos Substrate Barrier is made from non-toxic mesh and measures 18in x 36in. Our Substrate Barrier can be cut or folded to fit the bottom of your terrarium. A Substrate Barrier is used to separate your substrate and bedding from the false bottom in a bioactive vivarium. Before adding substrate on top of your Substrate Barrier, make sure that the edges of the mesh are snug to the sides of the enclosure. The Substrate Barrier should be placed on top of the false bottom and below the substrate. Using a substrate barrier is an essential part in keeping a clean and healthy bioactive terrarium.