You can get the flat rate bubble envelopes free from the post office, but you have to order them online and they deliver to your house. They are now made with a plastic outside and are 9 1/2 x 12 1/2. I still wrap the flap and edges with wide clear tape. Also one strip around the outside in the middle - supposedly protecting the address but really holding it all in. The new plastic envelopes cost just a little more to ship than the flmsy cardboard ones, but I think worth it.