The padded flat rate priority envelope has a red line on it ($5.90 to mail), while the padded flat rate priority express envelope has a blue line on it (about $20. to mail). They didn't have the cheaper one at my PO, someone on QB suggested I order it online, I was in a hurry to mail my package, looked at the USPS web site, ordered the correct size flat rate envelope, and received the one with the blue line, which was the only one I saw. I was not allowed to use it at my local PO for the cheaper rate, because it's the Express envelope. I went back to the web site and couldn't locate the correct envelope there. It's not on this page that I used before:
https://www.youtube.com/watch?v=fp34yI9SUeY ...and I used the search line and couldn't find where to order it either. So, it's sort of a tricky swap rule for me... I can use first class and pay for tracking-- takes longer though, and no insurance. I had to make an account to order the (wrong) envelopes, so maybe I'll order postage online next time, like Nelco. But I have to buy ink for my printer for that, I think. So many options!