I have looked at them in passing it feels odd to me as well. I use coco coir substrate so I am used to its feel. I might go to an actually greenhouse and talk with a knowledgeable clerk they may have better understanding of what else is in there. If it is safe for food crops I think it is fine for herps as long as it is free of fertilizer. You might check with the manufacturer. They often are very good (in general) responding to questions.