By Jessica Jones, How About Orange
Find an envelope of any size. (I embellished these by printing a label on the front of them first. You can use my design if you want; these PDFs are set up according to how my printer feeds envelopes through. If yours is different, you might need to experiment. Download the label for a small A2 envelope or a larger 6×9 envelope.)
2. Cut off one end of the envelope.
4. Put the bag over one hand. Use your other hand to shape a flat bottom for your bag, pushing the bottom center crease downward, causing the side folds to buckle out. Crease the corners of the bottom into triangles.