While ReptiChip is mold resistant, any wood based product (including paper) can mold under the right conditions of moisture and heat. Three things that you can do to ensure that mold doesn't take root: Increase aeration (hand sift the chips, and ensure that there is adequate ventilation in your tubs/enclosures).Ensure that the chips are not over saturated with water. If you squeeze a chip and more than a drop of water comes out, then they may be over saturated. To fix this, increase aeration, or add some dry chips to the mix. Diligently remove organic matter regularly (poop, sheds, etc. Regular spot cleanings are the best for this...any shed or poop is usually the first to grow mold under the right conditions...even rodent poop from live feedings will grow it first) and ensure that the enclosure is cleaned regularly with a reptile safe disinfectant (f10 or chlorhexidine).