The woman at the post office called me yesterday to let me know about the flat rate envelopes. The one woman thought flat in flat rate meant the envelope had to be flat. The other woman said no that is the rate that is charged. lol So she called yesterday to let me know they have had many conflicting emails about how thick an envelope can be. That's why different POs do it differently. So after much investigation they told me it's suggested it be no more than 3/4" thick and evenly packaged so it doesn't look like a football. It can be as thick as you can get it but they know the envelopes have a tendancy to break open if they are stuffed any fuller. She said since mine isn't going that far, it was ok to use the flat rate envelope but if it were going across country,and that thick, I should use the next envelope that feels like fabric. She said the envelope can get ripped open, especially on the corners and the contents may be lost. Just wanted to let everyone know this is supposed to be the official answer. But all PO are run differently. Hopefully, mailing mine today.