Build a solar cooker
Build a cardboard solar cooker to heat snacks or melt marshmallows using sunlight; learn about reflection, insulation, and safe sun powered cooking techniques.
About this activity
Build a cardboard solar cooker to heat snacks or melt marshmallows using sunlight; learn about reflection, insulation, and safe sun powered cooking techniques.
What you need
Step by step
- 1
Step 1
Find a sunny flat spot outside and set the closed cardboard box there.
- 2
Step 2
Cut three sides of the top of the box so one flap stays attached at the back to act as a reflector.
- 3
Step 3
Smoothly tape aluminum foil to the underside of the flap with the shiny side facing out.
- 4
Step 4
Tape black construction paper to the bottom inside of the box to make a dark heat-absorbing surface.
- 5
Step 5
Tape aluminum foil to the inside back wall of the box with the shiny side facing in to help reflect sunlight onto the bottom.
- 6
Step 6
Stuff crumpled newspaper or a towel around the inside edges of the box to add insulation.
- 7
Step 7
Cover the open top of the box with clear plastic wrap and tape the edges tightly to create a sealed transparent window.
- 8
Step 8
Tilt and prop the foil flap so it reflects sunlight straight onto the black paper inside the box.
- 9
Step 9
With an adult, place the oven safe tray with your marshmallows or snack on the black paper inside the box and close the plastic window.
- 10
Step 10
Ask your adult to check the snack every 10 to 20 minutes until warm or melted and then share your finished solar cooker and what happened to your snack on DIY.org
Fun facts
How do I build a cardboard solar cooker to heat snacks or melt marshmallows?
Start with a clean cardboard box and cut a flap on the lid, leaving one edge attached. Line the flap and interior sides with aluminum foil smooth-side out to reflect sunlight. Place a small black metal or oven-safe tray inside to absorb heat. Add insulation such as crumpled newspaper or a folded towel around the tray. Seal the top opening with clear plastic wrap or an oven bag to trap heat. Angle the foil flap to reflect sun into the box and test with an oven thermometer; rotate the cooker to fo
What materials do I need to make a cardboard solar cooker?
You will need a medium cardboard box with a lid, aluminum foil, black metal or oven-safe tray, clear plastic wrap or an oven bag, tape or glue, scissors and a craft knife (adult use), insulation like newspaper or towels, and a stick or small ruler to prop the flap. Optional items: a cooking thermometer, mirror or mylar sheets for extra reflection, oven mitts for handling hot trays, and simple snacks like marshmallows or sliced fruit.
What ages is this solar cooker activity suitable for?
This activity suits a wide range: children 6–8 can participate with close adult help for cutting, lining foil, and supervising cooking. Ages 9–12 can handle more steps independently, like arranging insulation and testing temperatures, under supervision. Teens can design improvements, measure results, and record data. Always supervise any use of sharp tools, hot trays, and food-handling steps, and adapt tasks to each child’s skill level and attention span.
Is building a cardboard solar cooker safe and what are the benefits or variations?
Solar cookers are safe with supervision: avoid direct eye contact with concentrated reflections, have adults use knives and handle hot trays with mitts, and only cook low-risk foods. Benefits include hands-on learning about reflection, insulation, renewable energy, and temperature measurement, plus science skills like hypothesis testing. Variations: pizza-box models, adding extra mirrors or mylar for more concentration, parabolic designs for higher temps, or using a thermometer to compare differ
Watch & Learn
Need help?
What can we use instead of aluminum foil, black construction paper, or plastic wrap if we can't find them?
If you don't have aluminum foil for the reflector you can tape on a shiny emergency blanket sheet or a clean reflective baking pan, substitute black paint or a dark towel for the black construction paper on the bottom, and use a clear oven bag or a tightly sealed large zip-top bag in place of the plastic wrap window.
My solar cooker isn't getting warm or the marshmallows aren't melting—what should I check and fix?
Make sure the foil is taped smoothly with the shiny side facing out and the back foil facing in, the flap is tilted to reflect direct sunlight onto the black paper, the plastic wrap window is sealed tightly with tape to trap heat, and the crumpled newspaper or towel insulation fills the edges so no air leaks cool the box.
How can I adapt this project for different ages so it's safe and fun?
For younger children have an adult pre-cut the box and attach foil and plastic while the child stuffs newspaper and watches, for elementary kids let them do the cutting and taping with supervision and check snacks every 10–20 minutes, and for teens add tasks like angle measurements and temperature logging with a cooking thermometer.
What are some ways to improve or personalize the solar cooker after we build it?
To enhance the cooker add a cooking thermometer on the black paper to record temperatures, create a double-layer plastic window for better insulation, decorate the outside of the box, and experiment with adjusting the foil flap angle to maximize sunlight and speed up melting.