Mylar is a polyester film widely used in archival storage of paper collectibles. Mylar D (also marketed as Archival Mylar or Mylar Snug) is chemically inert, does not yellow, and does not off-gas — making it the gold standard for long-term comic book, stamp, and document storage. Standard polyethylene and polypropylene bags are acceptable for short-term storage but should be replaced periodically. PVC bags should be avoided entirely.

Mylar is a brand name for biaxially oriented polyethylene terephthalate (BoPET), a strong polyester film that comic book and trading card collectors use as the gold standard for archival storage. Unlike polypropylene or polyethylene bags, Mylar is chemically inert, optically clear, and stable across centuries — properties that have led conservators and major museum collections to adopt it as their standard for paper-based archives.

For collectors, Mylar bags are the preferred enclosure for valuable comics intended to be held for decades. Mylar prevents moisture transfer, screens out a meaningful share of ultraviolet light, and does not become brittle or yellow with age. The trade-off is cost: Mylar bags are several times more expensive than standard polypropylene bags. Most collectors reserve Mylar for the highest-value pieces and use polypropylene for everyday storage. See how to store comic books for the full archival hierarchy.