Building a Solar Funnel Cooker

by Bruce Jacobs

You will need a piece of cardboard 2' x 4' or larger (can be cut out of a 2' square box), aluminum foil, white glue diluted 50% with water, 1 Reynolds oven cooking bag (large size preferred), a glass jar with lid, and non-toxic black paint. Also, a pair of scissors, a brush for glue/paint and some clear tape.

Cut out the 2x4 piece of cardboard (a larger size is ok) lay it flat

Find the center of one of the long edges.

Mark a 6'' half circle on the cardboard on one edge, like in the diagram below.
(does not have to be precise)

Basic Cardboard Cut
Basic Cardboard Cut

Cut out the hole. Save a 3-inch square of the cardboard.

Make series of folds in the cardboard radiating out from the hole like the Arizona state flag. Try to make enough so that there is a crease every 3-4 inches or less on the outside edge. (Precision is not important here either)

Cardboard with Creases Showing
Cardboard with Creases Showing

Lay it back flat and use the glue to cover one side smoothly with foil. Allow to dry. While it is drying, paint the outside of your glass jar and lid black. After the glue is dry, tape the foil edges down with clear tape. Then, roll it into a funnel where A touches D, and B touches C. with the foil inside. Tape it so it stays in this shape. Tape foil over the hole at the bottom of the funnel. Wait for a sunny day.

Put the food to be cooked in your glass jar. Point the wide part of the funnel toward the sun. Put the cooking bag in the funnel with 3-inch piece of cardboard inside. Place the glass jar on top of the cardboard inside the bag. Blow air into the bag to keep the bag from touching the sides of the jar where possible. Close the bag with a twist tie.

The food will get very hot. Adjust the funnel every 1/2 hour to point at the sun.

Cardboard with Creases Showing
Cardboard with Creases Showing

Safety Issues

  • Solar food gets hot!
  • Don't look at the sun, or stare at its reflection.
  • Use shadows to line up solar cookers with the sun.
  • Make sure paint used near food is non-toxic.
  • Don't use other plastics, they can melt.
  • Food containers may not look like they will be hot, but they can get to over 300F.

Adapted from