Ian is asking for origami envelopes appropriate for standard-size trading cards. Do you need it to be of the exact size or can there be a bit of leftover space inside? I think many rectangular models will work for you. You'll find different diagrams here: http://www.orihouse.com/elfa.html
https://make-origami.com/ELF/ Once you get the math behind the particular envelope, you can probably cut the initial sheet to the right size so that the final envelope end up with the dimensions you wish. I do advice that you add a few of millimeters, or sixteenths of an inch, taking into account the bulk of eight cards, There's one I like in particular, it's EnV DeloP, a variation by Michel Grand of Gay Merrill Gross's Merrill Envelope. That's because the model doesn't eat up too much of the original sheet, and in Michel's variation, you don't have to unfold the envelope completely in order to remove its contents. That means non-origamists will have no problem in opening and closing the envelope as many times as they wish. It has often happened to me that when I give certain types of origami containers to non-origamists, they end up with an unfolded and creased paper after opening it, which they don't know how to fold again nor have enough motivation to try. That's why I call those models containers for origamists ; ) If you're interested in that particular envelope, I suggest you contact Michel. Do you already know him? Cheers! -- Gerardo G. gerardo(a)neorigami.com instagram.com/neorigamicomKnowledge and Curiosity in Origami: six private classes online "(...) It doesn’t happen often, but when it does, it takes your breath away and fills you with the true joy of origami. I experienced this in my lessons with Gerardo G. I wouldn’t trade it for anything. Gerardo is (...)" C. R. Read the full review
