This is the lowly padded shipping envelope used by many. I use a lot of them and receive them too when I order something. I save the used ones from home and from work to re-use, but they look rather sad with all their old stickers and such. But there is hope for them! No throwing out perfectly good and usable items around here.
You can make them pretty, fun and cute like these!
I have a stash of 12" sq. scrapbook paper that I got on sale many moons ago and lots of it I will not use for scrapbooking. You could also use gift wrap, old maps, comics, newspaper, etc. Here's my cheap & easy way to do it.
Trim the end of your old envelope so it does not have a flap (I took the photo before I did that) and using plain old white glue (Elmers, etc) or even stick glue or double stick tape, dribble on one side of the envelope and stick down on the paper leaving enough paper at the top to fold over for sealing.
Then fold up the bottom and crease it, glue and press in place.
Next come the sides. Same thing of folding, creasing and gluing, only don't let your glue line go above the top of the original envelope, see the line I drew? I ran out of Elmers last night so this one is done with some double stick tape so I could show you.
Both sides now done. Don't worry about the spot in the center if you are working on a small envelope, the sticky labels you print will cover it. If you don't use sticky labels then you can just cut another piece of paper and glue in place. Once at this stage I use scotch tape to seal down those raw seams in the center and the bottom edge where the folds are. Glue is strong but you don't want edges that may hang up in their postal machines.
Once your item is inside, fold over the top and tape shut with packing tape, add your label and you're good to go!
You can even cut the large envelopes to a smaller sizes and get 2 or 3 from one. I do this as I usually only need small envelopes but tend to receive large ones as I order books. The ones from work are usually large too from Fedex or UPS. Those kind are plastic coated but they will work just as well. Pretty soon you'll have a box full to re-use!