Go to a PetCo or other chain store that sells reptiles, and ask a staff member what substrate you should use for a bearded dragon or leopard gecko. The worker will invariably tell you to use a calci-sand, Bone-Aid, or a similar substrate. Look in the cages on display, and you'll find they keep their own animals on such products. You'll usually see a large selection of sand substrates available in the stores.
The selling points behind these substrates are:
1. Your Gecko/lizards needs calcium and may benefit from occasionally ingesting the sand
2. The sand won't cause impactions
The problem is...
1. Your gecko/lizard should be getting its calcium from its diet and supplements.
2. The sand CAN and DOES cause impactions.
I honestly don't know why companies manufacture these products and stay in business.
Caci-Sand, Bone-Aid, and all the other sand substrates available are useless, and I do not recommend they be used.
You have a leopard gecko? Use paper towels.