I originally got one of the cardboard type envelopes, and the squares didn't fit, so I went back and asked for other alternatives. (I should have asked the first time I was there) Anyway, I got one of the strong papery envelopes from the clerk at the counter at the post office. I put 4 stacks of the 5" square in and it was the perfect width. There was even room in the end. Be sure to "burp" your ziplock bag so it fits in comfortable. It has to be weighed so they can't tell you what it costs until you bring it it and they weigh it. Mine cost $5.15 to send from SC to ME. I thought that was a great deal and I didn't even have to buy the envelope or label.