How to Make a Wonder Oven Insulated Cooking Box

Having enough fuel to keep warm and cook food in an emergency is an often overlooked area of preparedness.  One way to preserve fuel is to use an insulated cooker like the Wonder Oven (also known as a Wonderbox).  The Wonderbox was developed in the 1960’s by Anna Pearse, a South African philanthropist, for use in third world countries.  So there’s your history lesson for today.

The Wonder Oven works kind of like a thermos.  You put hot food in it and it continues to cook because of the insulating factor of the box.  I’ll do another post on cooking in the Wonder Oven (scroll to the bottom for the link to it!).  For today, we’re just going to make one.

The pattern I have is an adaptation of the original Wonderbox pattern by our local Extension Agent Christine Jensen.  Here’s the pattern (click on it to enlarge):

To make a Wonder Oven, you’ll need about 3 yards of standard 45″ wide 100% cotton fabric and polystyrene beads like found in a beanbag.  For the beads you can check with your craft store to see if they can order them bulk or just buy a beanbag and open it up and use the beads in it.  Read more on choosing a filler for your Wonder Oven here.  One standard adult bean bag fills two insulated cooking boxes plus a little extra.  For this Wonder Oven, I found a beanbag at a yardsale that was nice and clean, so picked that up cheap.  You would want to be careful buying used as you don’t want smoking or pet odors coming out when you cook your food–ick!  You can use any fabric as long as it is 100% cotton.  An old sheet, denim, etc. would all work.  I got some cute fabric because I’m making mine as a gift for a friend who has a music preschool.  I also thought that in a stressful situation, cute fabric might be a little pick-me-up.

I ironed my fabric to make it easier to work with, then laid out my pattern on it.  I originally laid it out like this, thinking I would just cut two of each piece on each side and have a strip of fabric left over in the middle, but when I got these two pieces on it and doubled the fabric back over the top to see if I’d have enough, it came out a little short, so my 3 yards wouldn’t quite make the box if I cut it out like this.

So I laid it out differently.  I folded the right edge over and placed the large bottom pattern piece on the fold, then flipped it over and repeated it on the left side.

Then I left a space large enough to cut one top piece out of the middle of the fabric and cut two more bottom pieces below that space.

I then left room again to take a top piece out of the center below the second set of bottom pieces.  Below that space I cut one top piece from each side of the fabric.

After I got those two top pieces cut out, I went back up and folded the fabric right down the middle and cut the two other top pieces out of the spaces I had left.

Cutting this way, I actually had fabric left over from my 3 yards after all 8 pieces were cut out.

Now we’re ready to assemble the pieces.  Get your large bottom pieces and lay two of them out right sides together.  You’re going to sew starting at the top point, down the side, ending at the bottom point.  It doesn’t matter which side you sew down because the pieces are mirror images of each other.  Pin them together before you start sewing.  Sew with a 1/2 or 5/8 seam allowance.  Just pick one and stick with it for the duration of the project.  It’s not like this is a fitted prom dress, it’s a pretty forgiving pattern.  Repeat with the second pair of bottom pieces.

Now we’re going to attach the two pieces we just made to each other.  Open them up and match the two pieces, right sides together.  Match up the raw edges, pin together and sew, leaving an opening near the top to turn and fill it.

Now, as is standard with sewing anything with corners, I trimmed and clipped my corners before turning the whole thing right side out via the opening, but it turns out that you really don’t need to do this.  I also recommend stitching over the whole thing one more time, so each seam is double stitched, just for good measure.

Now set the bottom aside and assemble the top.  Lay out two top pieces, right sides together and sew from the top point, down one side to the bottom point.  Repeat with the second pair of top pieces.

Then open the two top pieces up and pin them together, matching raw edges, and sew around, leaving an opening at the top to turn and fill through.  This is just like the bottom pieces we sewed together, just a little different shape.  Trim/clip the corners and turn it right side out.  To find the shape that the top and bottom are supposed to be, find where the corners all came together to make an X and flatten it out.  That is the top or bottom.  On the top pieces, it won’t matter which side is up.  The bottom piece, you want the big X down.  The smaller X will be the part that squishes inside the box to make a pocket for the pot.  See the X?

Now we’re going to fill the Wonder Oven sections with the polystyrene beads.  Get in a place that is easy to clean up.  The beads WILL go everywhere.  You can use a spray bottle with water in it to cut down on static–it won’t hurt anything.  This is easier with a friend.  Make a funnel to help get the beads in.  I used a file folder and taped it into a funnel shape.  Paper will work better than plastic due to the static.  Fill the top about half full of beads.  That’s plenty.  Really.

Fill the bottom about half full also.  I put mine in the box I was going to use for it and made sure the largest pot I’d be using fit in it.  Then I stopped putting beads in it.

Once your pieces have the beads in them, sew the openings shut.  You can hand sew them, but I don’t believe in hand sewing unless it’s entirely necessary, so I turned the edges in toward each other, pinned them together and top stitched them together.

There should be plenty of slack to get these openings sewed shut with your machine.  Now stick it in a box–a banana box or one of equivalent size works great–put the top on, and you’re ready to cook!  (Yes, it’s supposed to be a little loose and sloppy looking–that’s so it can conform to your pot shape/size easier.)

Still have questions?  I might already have the answer for you on the Wonder Oven FAQ page.  Now you have it built, check out the Cooking instructions here and get using it! :)

Keep preparing!
Angela

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