Adds environmental stimulus. Allows natural digging and burrowing activity. Provides your terrarium with that natural tropical rainforest look. Re USAble and super easy to maintain. Reptile bark should be replaced at least once a year. All natural made from the bark of fir trees. Hygroscopic. Absorbs moisture and then releases it into the terrarium, creating humidity. Perfect substrate for humidity loving reptiles. Provides better moisture retention.