Exo Terra Forest Bark Terrarium Substrate. The Exo Terra Forest Bark is a 100% natural, biodegradable reptile substrate made from sustainable wood bark. Forest Bark is the ideal decorative substrate for humidity-loving reptiles, amphibians and invertebrates from tropical and forest environments. Its hygroscopic properties regulate the terrarium's humidity in a natural way by absorbing and slowly releasing moisture. The unique size and shape of the bark particles stimulate natural digging and burrowing behavior, and discourage crickets to hide in the substrate. The fir bark is extensively tumbled to smoothen the bark pieces and remove dust, than heat-treated to reduce bacterial contamination. 100% Natural Douglas fir bark Controls air humidity levels Perfect for humidity-loving reptiles, amphibians and invertebrates Stimulates natural digging and burrowing behavior Heat-treated and odor absorbing Available Sizes: 4qt / 8qt / 24qt