Mylar vs. polyethylene vs. polypropylene: choosing the right comic bag

The question comes up constantly on collector forums, at conventions, and in specialty shops: which bag should you choose to protect your comics? Mylar, polyethylene, polypropylene — the terms pile up, opinions diverge, and between cheap 100-packs and eye-wateringly expensive Mylar, it's easy to get lost. Yet the bag choice is one of the most important decisions a comic collector makes: poor protection can destroy in a few years a comic that took years to find and is worth hundreds or thousands of dollars.

This comparative guide gives you everything you need to pick the right bag by comic type, budget, and preservation goals. We analyze each plastic type in detail — its chemical properties, lifespan, and ideal use cases. One absolute rule to remember right now: never PVC.

Bag types: understanding the materials

Mylar — the ultimate protection

The term Mylar is actually a trademark owned by DuPont for a biaxially-oriented polyester film (PET: polyethylene terephthalate). In the collecting world, "Mylar" is used generically for any polyester preservation film. You'll also see Blylar (Blystal brand) and Melinex (ICI/DuPont brand), which refer to equivalent products.

Mylar is the reference preservation material for archives, national libraries, and museums. Its properties are exceptional: chemically inert (emits no gas, no plasticizer, no harmful molecule), estimated lifespan over 100 years without significant degradation, UV resistance superior to polyethylene, excellent moisture barrier, and perfect optical clarity that lets you read the cover without removing the comic from the bag.

Mylar is rigid and crinkles slightly when handled — a trait that identifies it immediately. It typically comes in two thicknesses: 2 mil (50 microns) and 4 mil (100 microns). 4 mil is recommended for your most valuable comics; 2 mil for important but not exceptional books.

Polyethylene — the accessible standard

Polyethylene (PE) is the plastic most widely used in standard comic bags. It comes in two variants: low-density (LDPE) and high-density (HDPE). For comics, LDPE is typically used, offering suitable flexibility.

Polyethylene is relatively chemically safe — it doesn't emit chlorine like PVC — but it has several important limitations compared to Mylar. Its lifespan is estimated at 5 to 10 years before it starts to degrade and become brittle or yellowed. It lets more moisture through. Its UV protection is inferior. It scratches more easily, leaving micro-scratches on the cover in contact with it.

Polyethylene remains the standard choice for ordinary comics in your collection — issues you reread regularly, run fillers with no special value, and recent acquisitions awaiting final classification. Its very low price ($2–$6 per 100 bags) makes it indispensable for large collections.

Polypropylene — the unsung middle ground

Less talked about than its two competitors, polypropylene (PP) is still an interesting preservation material. More rigid than polyethylene but less so than Mylar, it offers intermediate protection with an estimated lifespan of 15–20 years — better than polyethylene, not as good as Mylar. Its cost sits between the other two materials.

Polypropylene has excellent optical clarity and good chemical resistance. Some premium "polyethylene" bag brands are actually polypropylene — always read the exact composition on the package. For comics of intermediate value ($55–$220), polypropylene is a good compromise between protection and budget.

Comparison table: Mylar vs. polyethylene vs. polypropylene

When to use Mylar and when to use polyethylene

Always use Mylar for:

• All Silver Age comics (1956–1970): These issues are rare, valuable, and fragile. The paper from this era is often already degraded and requires the best available protection.
• All key issues, regardless of era: first appearance, first issue of a major series, any comic worth more than $110: Mylar is required.
• Comics destined for CGC/CBCS grading: before sending a comic for grading, keep it in Mylar to minimize damage risk during shipping and waiting time.
• Valuable Bronze Age comics (1970–1985): paper from this era often shows "tanning" (natural yellowing from paper acid) that accelerates with poor protection.
• Comics in Near Mint or Very Fine condition: if you've acquired a book in perfect shape, don't downgrade it with poor protection.

Polyethylene works for:

• Modern run fillers (post-1990): comics published since the '90s use higher-quality glossy or coated paper, less susceptible to short-term degradation.
• Comics worth less than $22: the cost of Mylar isn't justified for ordinary comics.
• Temporary storage before sorting: during convention or flea-market hauls, a polyethylene bag while awaiting final classification is enough.
• Duplicates and extras: comics bought as duplicates for future resale or separately stored variants.

Recommended bag brands

Not all Mylar bags are created equal. Here are the brands that have consensus in the collector community:

For Mylar

• E. Gerber Products: the absolute reference in the US, recognized by CGC. Their "Mylite 2" (2 mil) and "Full Back" products are the pro-market standards.
• BCW Supplies: good alternative, slightly cheaper, widely available.
• Ultimate Guard: European brand of quality, good availability.

For polyethylene

• BCW Supplies (poly bags): the market standard, good price/quality ratio.
• Ultra-Pro: very widely available, decent quality for ordinary comics.
• Dragonshield: more oriented toward trading cards, but some formats suit comics.

Backing boards: the essential complement

A bag without a backing board is useless. The comic can bend, warp, or develop marks inside the bag. Essential rules for backing boards:

• Acid-free is mandatory: standard cardboard backs contain acid that migrates into the contacting cover. Use exclusively acid-free boards ("acid-free" or "pH neutral" must be marked on the package).
• Replace them regularly: even acid-free boards acidify over time (2–5 years depending on quality). Replace them during your collection reorganization sessions.
• Right size: the board must match your bag format: Current, Silver Age, or Golden Age.
• Double-board for key issues: for very valuable issues, some collectors use two boards (front and back of the comic) for maximum rigidity.

The most common mistakes to avoid

Budget and supply strategy

For a 500-comic collection, here's a realistic 2026 budget strategy:

• 50 Mylar 4-mil bags + 50 acid-free backing boards for your 50 key issues and valuable books: roughly $33–$55 depending on brand.
• 450 polyethylene bags + 450 acid-free backing boards for the rest of the collection: about $28–$44 for bags, $33–$55 for boards.
• Total protection budget for 500 comics: $95–$155, to spread across supply purchases at conventions or online specialty retailers.

Buy in bulk — unit prices drop sharply starting at 100 bags. For Mylar, prefer 50-packs to start rather than prohibitively priced 10-packs. Check our guide on beginner collector mistakes to avoid other common traps.

FAQ: Comic preservation bags