Solar Cookers International has received many inquires raising concern about the chemical composition of the underside of lids of jars when the jars are used for solar cooking vessels. The experts we contacted on this subject, the best advice we could get was to suggest that you contact manufacturers of jars/lids in Taiwan to see what they could tell you about composition and toxicity. Will the polyvinyl coating on the underside of a lid used in solar cooking reach over 121°C? We don't know, but it seems plausible to us. What happens to PVC at that temperature? We still don't know that, either.