The Lucky Reptile Humus Brick consist of natural coco humus which has been pressed to a tight brick. If placed in water, this humus brick will swell up to about 8-10 times its volume. The humus is excellent for burrowing animals and can be used either dry or humid. It is an excellent substrate for tarantulas and tortoises as well as tropical amphibians and reptiles. The Lucky Reptile Humus Brick is a natural product (100% bio degradable) and free of chemicals, pesticides or fertilizers.