I manufacture and market a 100% all-natural bentonite clay-based mask that is very rich in essential oils, powdered herbs and has added zinc oxide, coconut and olive oil. I have no issues with mold (thanks to rosemary and tea tree oils) but am experiencing shrinkage in the plastic polypropylene (PP) 16 and 8 oz containers that are due to either heat or rough handling during shipping. I have several distributors and the problems are coming from Amazon fulfillment and another very large company that will not handle the products any differently than any others. Product is that shipped by me or other smaller distributors have had no issues. Is there something I can add to the formulation that will help the product retain its shape? The products are hydrated with apple cider vinegar, no water, but of course the ACV is a dilution. Thanks.