Here's an FYI. I looked on
www.usps.com yesterday to find out the postage rate for the Priority flat rate box that is about 11" x 13" x 3" - in order to mail a quilted item to a friend. It was $10.35. When I got to the P.O. today, I could not find those Priority boxes (that are free), so I put it in a large (Tyvec) Priority envelope (also free) instead. The postage was $4.95 - even with insurance and delivery confirmation it was far less than $10.35, and I feel pretty confident that the item will be just fine - I had already put it in a Zip-Lock bag. (As I was standing in line, after I had already sealed the envelope, I looked up and saw the sample boxes, numbered, on a shelf above the workers' heads. I guess you decide which one you need and tell them the number and they get it for you.)