After my father went off to fight Hitler in 1944, my grandmother did the one thing she had long wanted to do: She cleaned her son’s room. Into the trash went mementos of my dad’s childhood, including several shoe boxes filled with comic books. This collection included a copy of Action Comics No. 1, the book that introduced the world to Superman in 1938.

A pristine copy of this comic book sold at auction in 2014 for $3.21 million on eBay.

But that was all in the future. Back in the 1940s, Dad returned from World War II, inspected his room and had one question: What had happened to his comic books? To this day he laments the loss (especially Action Comics No. 1). He often wonders if he had only packed them more carefully, maybe his mother would have realized their importance.

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Here are some tips for safely storing your comics, courtesy of Nick Purpura, co-owner of JHU Comic Books in New York City, Ron Gandy, co-owner of Velocity Comics in Richmond, Virginia, and comicvine.com.

Bag 'em. Purpura says serious comic book collectors follow several tried-and-true methods for keeping their books safe for years to come, including getting a supply of protective bags in the correct size for their comics. Bags come in four sizes corresponding to the four main periods in comic-book history: Golden (approximately 1930 to1960), Silver (1960 to 1970), Regular (1965 to 1980s) and Current (1990 and beyond). It’s a good idea to measure the books before selecting bags, though, because there is some overlap in publishing sizes in these periods, he notes.

Save the Mylar for your most valuable comics. Purchase archive-quality storage bags made of Mylar, polyethylene or polypropylene. These materials are acid-free and designed to protect paper. Mylar is the most expensive but lasts the longest. You want bags with a flap on the back that can be secured with a piece of tape. This way, nothing comes in contact with the comic inside.

“Mylar is expensive for storing day-to-day comics,” says Gandy. “We have polypropylene bags that work well, and we’d recommend Mylar for the most valuable books in your collection.”

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Purpura shares this opinion. “Mylar bags are made of the thickest material, and they’re made to last,” he says. “Paper from the ‘30s to the ‘60s is thinner and more fragile, so you want something like Mylar to protect those books."

Avoid garage and attic storage. “Always store at room temperature,” says Gandy. “I see a lot of collections people have pulled out of garages and attics. The pages are brittle and yellow from the heat.”

Purpura agrees that you should keep the comics clear of light and heat. “You leave something red in the window for a week and it’s going to come out pink,” he says.

Handle with clean hands. Wash your hands and dry them before handling valuable comics, Gandy says. Skin oils, dirt and moisture can cause havoc on paper over time.

Board your books. Boards are acid-free card stock that provide support for bagged comics. Having a board behind the comic makes it harder for the book to be bent or folded. Boards typically have a rough side and a smooth, glossy side. Place the smooth side against the back of the comic before placing it in a bag. “You put a comic in its proper size bag with a board and that should be more than enough,” Purpura says.

Box 'em. Bagged comics should be stored in a box to prevent sunlight from fading the covers. Relatively inexpensive boxes made of cardboard are available at office supply and comic book stores. Store comics upright. When laid flat and stacked, the pages can become stuck together. It’s also easier to locate and retrieve comics stored vertically, says Gandy.

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Steve Evans, MA, is an award-winning journalist with more than 20 years experience in daily news, investigative, health and business journalism. Among other jobs, he has served as managing editor of the Central Virginia Newspaper Group, as a senior writer for SNL Financial and as a staff writer for The Progress Index and the Richmond Times-Dispatch.