I had this long conversation with a large dealer in archival storage materials. They claim that the plastics used in the hard type holders such as "Air Tite" or "Safe", as well as "Mylar 2x2s" are safe to use for storing copper. I'm looking for some of you copper dealer members to weigh in on this issue. Cotton and paper envelopes? Mylar 2x2s? Archival plastic? What's the professional consensus?