Not exactly sure what it is, but I know that its not the problem, people keep reptiles on it and my breeder keeps all his mice, rats and ASF on it, its Lignocel JRS is the company, its a German company. I have been keeping all my rats and mice on it no problem, I just think I got some sick ASF's the first time, the second group I got had no issues at all and have already had one litter, although the mom let them die, Ive had them on it for a few months, its the new ones I just got I noticed sniffiling on one again.