Protecting your investments is as important as selling them. You’ve spent money buying it, time cataloging it, and effort uploading it to the internet or printing it in a catalog – So, you want that item to stay in the same condition it was when you acquired it. Delicate items like: books without boards, collectible grade vintage paperbacks, leather that has started to deteriorate, paper items, ephemera, photographs, posters, non book items – things that can tear and lose integrity from just being stored next to one another. Putting a layer of any archival grade polymer around it, will allow the item to SLIDE intead of tear. It will also keep loose spines and boards together with the book.
The best part is that Polybags now come in an infinite number of sizes and thicknesses. The easiest & cheapest to find are comic book bags (and backing boards). My comic vendor also stocks Magazine and newspaper size, but almost never has paperback size. Those I have to special order in bags of 100 or 500. if you only need a few, eBay Vendors stock the various sizes.
Ultra-Pro seems to be the most popular maker for the comic trade, they make items to protect almost any sporting or not sporting collectible. (I use lucite baseball card boxes for all sorts of storage)
Bagsunlimited.com stocks every variation and thickness under the sun, they aren’t the cheapest on the net, but they do carry a lot of odd things, like Rolled Poster bags etc. Their Catalog is a masterpiece of merchandising.
Compare adding a fifteen cent bag to a delicate item, with having to dress down that item after it has been damaged in storage? It is worth the investment to have these things on hand while you are cataloging.