Yeah, those cardboard flat rate envelopes have given me a lot of trouble. I don't know if it's the Georgia heat, the humidity, or what, but the flaps always seem to pop open. The adhesive they use just doesn't hold up. On top of that, the cardboard tears easily.
Just recently I ordered some charm packs from an eBay seller, and she shipped in a cardboard mailer. The package arrived in one of those "Oops, we're sorry" bags from the post office (I call them "body bags" - LOL!), because the envelope had torn open and the charm packs fell out. Luckily one of the post offices that they passed through along the way managed to round all the charm packs up, so nothing was lost.
Anyway, I just order the padded mailers now. They're much more durable and the adhesive stays stuck. And they seem to hold a lot more stuff.
