This project has been kicking around on my desk for a few months now, so thanks to scoochmaroo for giving me a much-needed push to finally write it up. This project started when I was looking for a way to make microwave popcorn from scratch. It's easy enough to find microwavable paper (wax paper, parchment, oiled brown paper), but any adhesives that would close a bag (staples, glue) would definitely not work in the microwave. It seemed like a perfect opportunity to use paper folding as a structural technique to make an attractive and functional microwavable popcorn bag. I tried making popcorn in the first origami model I ever learned: a paper balloon. It worked like a charm. The popcorn popped and inflated my balloon perfectly. The only problem was that the serving size was a little small to be practical. And I couldn't help but imagine an attractive origami model that popped up into a perfect popcorn bag.After many, many crumpled up sheets of paper (and a few messy spills in the microwave), I finally worked out this design. It works, it's cute, and heck, it's even reusable! I've made a few of these as gifts-- I love the idea of giving someone a card that they can microwave and turn into a snack. I even designed some cute tags to attach with instructions for popping (pdf attached).

Step 1: Materials & Ingredients

a 12"x18" piece of plain (not recycled) brown packing paper*
non-stick cooking spray or oil
paper towels
a ruler
scissors
popcorn
high-heat cooking oil (such as canola, avocado or grapeseed)
salt (optional)

*There are lots of tutorials out there suggesting that you can use an ordinary brown paper bags to make popcorn in the microwave (including one published in the New York Times). Paper bags are convenient, to be sure, but I had a hunch that they might not be entirely safe for cooking. Turns out the USDA agrees with me. Their guidelines advise against using brown paper bags. Recycled paper and adhesives can release fumes when exposed to heat, that you wouldn't necessarily want in your food. The USDA suggests buying paper bags made particularly for cooking (only I haven't been able to locate any). Obviously you've got to make the call about what cooking materials you feel safe using. Paper can be safe for cooking, and coating it in oil (as I suggest) reduces the risk of scorching. But you do want to avoid extra, nasty chemicals that might be used to process them. I used (not recycled) brown packing paper. My best guess is this is about as safe a cooking paper as you can find, and I'm comfortable using it. The call is obviously yours.

You can also make this design using wax paper or parchment paper, though it is flimsier and harder to fold. If you decide to make this bag out of wax or parchment paper, you'll have to make a few modifications to the process. In step 2 cut 2 sheets of paper, exactly the same size. Skip step 3 (parchment and wax paper don't need to be oiled). Complete steps 4 and 5 separately out of each sheet of paper. Once you have 2 paper tubes, slide one inside the other, staggering the overlapped side. So the top of the innermost tube will be next to the bottom of the outermost tube. From this point on fold the two sheets together as if they were one.

Step 2: Cut Paper

Measure and cut your paper. I used a 12"x18" rectangle, but you can make a bag that is a little bigger or smaller. Just make sure that the long side is 1 1/2 times as long as the short side.

Divide the long side of your paper by 10, and mark this interval along both sides of your paper. For my sheet, a tenth was 1.8", so just over the 1 3/4" mark.

Step 3: Oil Paper

Spray brown paper with non-stick cooking spray or an oil sprayer, or lightly dab the sheet with oil until the surface is even and saturated. Your paper will feel less greasy and be much neater to work with if you use just enough oil to saturate the paper, and if you let the oil sit for an hour or so before folding. If there is any excess (shiny) oil remaining when you want to fold, use a paper towel to blot the paper.

Step 4: Set Up Folds

Zig-zag fold your sheet of paper aligned with the markings you made earlier. You should now have a zig-zagged piece of paper with ten equal rectangles. It's easy to rush this step, but the more precise you are with these set-up folds, the prettier your card will turn out.

Step 5: Fold Zigzag Into a Tube.

Fold zig-zagged paper over to make a tube. There should be 4 equal sides to the tube with a crease in the middle of each side. One side will be an overlap of the ends, so it will be double thickness. I'm calling the side with the overlapping paper the bottom, and the side opposite the top. Pleat the sides and lay the tube flat. It should look something like a paper lunch bag.

Step 6: Fold Diagonal Squares

Fold the rectangle in half, forming a crease down the center. Use this crease to align a diagonal, and crease along that diagonal line. Make another diagonal crease going the opposite direction.

Use these two diagonals to align a vertical crease-- this crease will mark a square. Use this crease to align two more diagonal folds along the edge of the paper.

Repeat these folds on the other side.

Step 7: Open Ends

Your model now has 2 complete squares in the center, flanked by a little more than half of another square. Make a vertical crease through the middle of one of the center squares (see pictures). Fold the whole side of the model straight up. Stick your hand inside the edge of the model and open the ends of the model as you would open a paper bag. Spread the folds out along the creases until the model has a flat, square base (think the bottom of a paper bag) with four sides sticking directly up.

Repeat with the other side.

Step 8: Pinwheel Fold the Ends.

Fold each edge of the "paper bag" sides down and over to the right. Because these pieces interlock, you might have to unfold and refold to get all of the fold to lie flat. Eventually each corner crease should align with a side of the square base. Now the sides will interlock into a pinwheel configuration.

Repeat the pinwheel folds on the other side.

Step 9: Fold Pinwheel

Each pinwheel has four flaps. Unfold one flap and ,starting at the outside edge, fold the flap underneath to align with the diagonal crease. Make a second fold, this time starting at the center of the pinwheel. Again, fold the flap in half, aligning the edge with the diagonal crease. Fold the flap back to its original position.

Continue on to the next flap, making the same two folds. Work your way through all the flaps in this manner until all the edges are neatly tucked under and you have an attractive pinwheel pattern.

Repeat with the other side.

Step 10: Fill & Pop

Unfold one end of the model so that the end is sticking up. Lightly coat 1/4c. popcorn kernels in cooking oil and sprinkle with 1/2 t. salt (optional). Scoop the kernels in so that they fall into the cavity of the model. Shake and rearrange the bag so that the kernels are evenly distributed. Refold end as before along existing creases.

Step 11: Pop

To cook:
Lay bag flat, with the folded ends facing up. Microwave on high for 2 minutes, until there are 5 seconds between pops. Now your bag will have inflated and filled with tasty popcorn! Sprinkle with desired seasonings and shake closed bag to distribute.

*You might be tempted to add other seasonings to your popcorn when you are filling the bag. (I was). From experience, it is better to add seasonings after you have popped the corn. It is very difficult to evenly distribute any seasonings in a way that does not cause them to burn in the microwave. If you are making the pop up card as a gift and want to add flavor, make a little envelope and fill it with seasonings to add afterward.