As a long time card collector/ trader as well as former postal employee, I'm seeing a lot of people wasting postage and other people risking getting their cards damaged in machines and or returned for inadequate postage. Here are some things to know and best ways to ship PWE (and also abide by the USPS guidelines, which I'm all for bending the rules if you wanna risk it and do have a few tricks thaht I use , but here is some legitimate, cost effective way(s) to ship PWE and not get damaged or returned .
First off, you shouldn't be using forever stamps on pwe's at all unless it is with standard cards that are in nothing more than a penny sleeve.
If youre using semi rigid or top loader (never have an envelope exceed 1/4 inch).,
THIS is the stamp you should use. Read the last paragraph on that page for more info. It covers rigid (non bendable) envelopes and the extra charge covers the cost of handling manually and it does not go in a machine that can mangle your card prottector).
If your envelope exceeds 1oz, don't put another butterfly or a forever stamp on there. Stock up on additionl ounce stamps. They are 24 cents and you can use up to two (envelopes should not exceed 3 oz).
Something I would recommend experimenting with- cut the top row and the side with the 3 holes off of a 9 card Ultra Pro page and put multiple cards in the pockets with a tiny piece of tape over the slots and fold in half and put in a standard size envelope. I mail about 15 low value singles this way for $1.54 (1 non machinable butterly stamp, plus 2 add'l oz stamps).
Another thing (nothing to do with USPS) I'd recommned is do not use scotch tape. Surely youive received stuff taped with it, and know it's a pain in the ass. Use blue painters tape. It's $1.25 at a place like Dollar Tree and peels off easy with no residue.
One number to remember is 0.4oz which is the weight of a standard card in sleeve and top loader with a tiny bit of blue tape at the top. So, two of those in a small Mead #8 envelope usually weighs exactly 1 ounce.
I reccommend spending a few bucks on
one of THESE. I paid like 10 bucks for one years ago and it saves a lot of worrying about being over or adding stamps unnecessarily.
I know this could be laid out in a better format but I kinda just typed it quickly off the top of my head hoping to help some people who are a bit unsure or misinformed.