What Is Substrate?

Substrate is just the material that is used on the bottom of the enclosure.  The type of the substrate used on the cage floor can vary enormously from newspaper which is cheap and easily replacable, to sand and sphagnum moss. Other substrates include crushed walnut shell which is very hygienic, bark (which bobtails like to burrow under), calcium sand (which is safe to digest) and astro turf works well with frogs.  It depends upon the requirements of the particular species and your personal preference.