Why do leopard geckos need sand at the bottom of their cage?

Sand is the leading cause for impaction. Once the animal ingests sand, it can build up in the digestive tracks and the animal won't be able to pass it. Once impacted, most animals will not eat or drink due to the pain and this can lead to death. Most breeders do not reccomend loose substrates for this reason.

Depending on the species, Papertowel is a great source for holding moisture as well as it is very easy to clean and dispose of, as well as affordable.