Board Thread:Fan-made Monsters/@comment-27950421-20160712201128/@comment-27950421-20160717041628

Substrate is what you have lining the bottom of the enclosure. Most folks use sand, repticarpet (basically astro-turg), Sand made from ground up calciun and a variety of mulch type stuff like chips of wood bark or a moss type stuff. Hell, even folded up paper towels are a type of substrate.

Bioactive substrate is one of the more complex types of substrate, it uses rocks, sand, dirt, and water to mimic the soil strata in the wild. It can be difficult to pull off but it usually works very well in keeping the animal healthy and you can grow plants in it as well. It does have a bad reputation though. In the captivity reptiles don't move as much so bits of dirt that get eaten with the food don't get worked out of the animals system so the animal can get impacted (basically its digestive system gets clogged up with debris resulting in the animal getting very sick and eventually dieing). This can be easily remedied by simply feeding the animal in another enclosure (a common practice amongst reptile keepers), hand/tong/tweezer feeding the animal, or in the case of most snakes, putting the food in a small bowl. However the possibility of impaction combined with idiots who accidentall poison their pet by using potting soil with fertilizers and/or pesticides and even bigger idiots who think that a bioactive substrate means that they don't have to clean up the snakes poop has resulted in most herp keepers mistrusting the system.