Cardboard is a popular material used for the construction of solar cookers. Can easily be found for free in developed countries and relatively cheaply in poorer countries. It is ideal for solar cooking because it's lightweight, easy to work with and easy to find. Double-walled corrugated cardboard is stronger and more insulative than single-wall, desirable characteristics for some types of cookers.
Boxes from electronic equipment such as computer cases, printers, laptop computers, etc, are often of superior quality and in good proportions for solar box ovens. Stores that sell window glass and doors are good sources of long pieces that are useful for cutting 'planks' for liners or for other applications where long or large pieces are needed. Take a box or razor knife, straight-edge, and cutting board/mat along with you on quests for long/large pieces, so you can cut them down to a size that will fit in your vehicle if necessary. Cardboard cookers can be made more water-resistant by painting them with several coats of exterior latex (check with a recycling center to see if there is a program in your community to recycle paint—you may be able to get free paint for your cookers!). This doesn't mean you can store your cooker outdoors full time, but it will make it more resistant to dew or unexpected light rain that might blow in while your cooker is out. For greater strength and water resistance, the fabric/glue/beeswax treatment described on the Tips and Tricks page is very good. You still can't store your cardboard cooker outdoors all the time, but it will take more in the way of dew or an unexpected shower that blows up while you're away from home, and it makes the box very tight and strong.
Working with Cardboard
- Measure twice, cut once! Be sure your line is drawn right before cutting.
- Use a box or razor knife with a sharp blade.
- Use a straight metal edge to cut against. A rafter square, which is an L shaped ruler, is very useful for measuring, cutting, and making sure angles are square.
- Go over your line repeatedly, rather than trying to cut all the way through on the first pass. The cut will be straighter and easier to control if your first pass is very light and shallow.
- Main article: Glue
- A half and half mix of water and white glue works well for gluing cardboard and foil together.
- Cheap sponge brushes work very well for spreading glue smoothly on cardboard or foil and are suprisingly easy to clean afterwards. A very smoothly folded piece of worn, smooth cotton is the best thing for smoothing out the foil when gluing.
- When gluing cardboard to cardboard, wood glue may give a stronger result than white glue.
- Main article: Paint
- Sponge brushes work very well for a smooth result on cardboard. Get them just a little damp (wet, then press excess water out with hands) before painting.
- Exterior latex is good for the outside of cookers. Use thin coats and let dry before the next coat so your cardboard won't get wet enough to try to warp.
- For painting cardboard black for oven interiors, use black tempera paint mixed with some white glue.
- Main article: Waterproofing
Stephen Pearson reports: "We build CooKits in pieces use eleven small panels of cardboard. Shops even in rural areas have thin cardstock available as scrap. These can be laminated together using local cassava glue (cassava is grown all over Africa) to form stiff panels, thus avoiding the need to import thicker cardboard. Join the eleven panels together with 2" strips of worn out dress or shirt (using the cassava glue). Protect the perimeter of the 11 panels with more 2"strips (1" front and 1" back to stop delamination of the cardboard). Let each panel dry properly. Then turn it over and glue on the aluminum foil to the side with no cloth hinge strips."
- November 2007: University students put corrugated plastic to the test - Solar Cooker Review