Mylar v. Poly: Bags of Justice
There is a piece of conventional wisdom amongst comic book collectors. Mylar bags are better than poly bags. Mylar bags are used in the Library of Congress. Poly bags need to be replaced every five (?!) years whereas Mylars last ages. I have comics in my collection that I have personally owned for over 30 years, some in poly and a few in mylar. I thought it would be worth taking a look at how the books held up over the years.
I started with Superman: The Man of Steel #1. The start of the weekly books in the 90s. The beginning of a great run on art by Jon Bogdanove. The copy on the left has been in a poly bag since 1991. The copy on the right in a thin mylar. The mylar bag at this point is very fragile. It tore a bit when I was putting the book back in. The poly bag though feels just like new. One of the complaints I’ve seen about poly is the way you get lines as it ages. You can see those in the glare on the left. I typically see this on books that are bagged tightly. Nowadays I’m using silver age sized bags for my modern books. This way they aren’t squeezed in so tightly it looks like they will burst. Also helps with prestige format books or those 100-page giants. The mylar on the other hand crumbles. and stays wrinkly. Easily visible in the glare here. I don’t see any color difference between the two copies. Any color difference in this picture is just lighting in the room. To the naked eye they look identical. The only problem I have is it looks like someone named Jon Bogdanove wrote his name on my mylar bagged copy (humble brag)!
So I opened it up to look at the pages. Are they yellowed? Have the colors faded? No on both accounts. They both look identical and look just as awesome as they did almost 30 years ago. Because of the crumpling I’d say in this case poly wins! Bog’s Superman is so great.
Next up Action Comics #591. One of my favorite issues in the Byrne run. The Legion of Super Heroes tie in books are also awesome. Poly on the left, mylar on the right. Again (more humblebrag) some John Byrne wrote his name on the cover of the mylar bagged version. Again cover color quality between the two copies were identical. Any differences once again being due to lighting in the room.
Page quality looks identical between the two copies again. I picked a page that was mostly white to see if the pages turned yellow at all. This 33 year old book looks great.
The Adventures of Superman #441 is next. 32 years old. Once again poly on the left, mylar on the right. And once again I couldn’t find any differences in the quality of these two covers. Both look great. This is an awesome Mxyzptlk story and Ordway is a legend.
Opening it up we see what is possibly the first Streaky The Supercat appearance Post-Crisis. Colors in both copies held up and the yellowing of the pages are also identical. Both look great.
Superman #50 from 1990. The mylar bag seen on the right is one of the thicker bags. One that will stand by itself versus the floppier ones shown earlier and the poly bags. Major down fall to that is you can’t fold over the top to close it. I know some mylar bags aren’t like this, I’ve got a copy of Superman 252 in a thicker Mylar bag that has a flap.
Colors on the cover and of the issue were consistent between the two copies.
A difference I did notice was on the edges on the back. The version in the poly bag had some wear on the edge. The solid mylar didn’t. This could have been from before the books were even bagged, but it would be logical that the more solid bag would prevent bends.
For fun here is a copy of the recolored second printing. Not bagged or boarded! Blasphemy!
I thought I might take a look at two newer books to compare how the poly bags had worn down. The beginning and the end of the New 52 with Action Comics #1 and Action Comics #52. Nine and four years old respectively. Neither of these bags looked like they needed to be replaced or had any wear on them. Despite suggestions that bags should be replaced every five years. 
I’ve seen YouTube videos with collectors claiming using poly bags will make your book imprint on the backing board. Not happening here on either of these issues (or any of the old issues I looked at).
It’s hard to come to any conclusion but that the hype on mylar bags is just that. Hype. They are considerably more expensive and in my experience added no additional benefit. Of course this isn’t a double blind scientific test. There are so many factors that come into keeping comics in good condition. It’s possible that under less than ideal conditions (basements, attics, storage units) a mylar bag would add additional protection. But in standard apartment conditions that I’ve lived in the last 30 plus years my books have kept up in decent shape. I will say that the thicker mylar bags have a nice presentation to them. If you are displaying books in anyway there is a small benefit there.
Since I was looking at books I had multiple copies of from the 90s I ended up pulling out all my copes of Superman #75. Two unopened collectors editions, two opened collectors editions (one bagged not boarded, the other the one my mother brought to me at school the day it came out), two newsstand editions (one bagged and boarded the other loose), three unbagged fourth printing copies, and finally an unopened Platinum Edition in a thick mylar. No wonder this comic sold as well as it did!
