Bow-legged Cards
 

You know, when laid flat on a table the top and bottom edges slightly arch toward the center. They are all Topps, when a series was printed on thin stock, and were stored in veritical stacks for a couple of decades. A half dozen years ago they were put upright inside penny sleeves inside a toploader. Still the same shape. What's the remedy?

That's a good question, Paul, as I have some modern cards that do this.

I've tried the penny sleeve + toploader, and putting a heavy book on top of the cards, and the curl remains.

We don't want to risk damaging the cards, but there has to be a way to straighten them out.

Suggestions, guys?