How to make a sun-powered marshmallow roaster

Solar marshmallow roaster

This is a really easy contraption to make. All you need is a cardboard box, foil, and page magnifier. It is a hassle free way to toasting marshmallows, you don’t have to go though the entire process of lighting up a campfire. It is also ecofriendly as you will be using waste to make something new.

A cardboard box comes with many appliances and is usually discarded. It is a good idea to put it to use. Although the Frensel lens is flat, it does have ridges and curves on one side which helps the sun rays to bend. The white marshmallow reflects most of the light concentrated by the roaster and absorbs only a speck of it which is enough to heat it up. To burn the marshmallows instantly just place it on the tiny spot where sunlight is concentrated. The marshmallow will immediately heat up here turning black, a color that readily absorbs light. So keep the marshmallow close to the tiny spot if you like it well done otherwise a little further away.

Difficulty Level: Easy

Time required: 20 minutes

Resources required

1. Aluminum foil

2. Cardboard box

3. Page magnifier or Fresnel lens

4. Bamboo skewers

5. Tape

6. Glue

Estimated cost

There is hardly any cost involved in making this device. All these materials are easily available at very affordable rates. In fact you might already have some of the materials lying around at home.


1. Cut out holes on one side of the box. The dimensions of the hole should be about ¼ inch smaller than the length and breadth of the lens. So when the lens is glued on it will just cover up the entire hole leaving no gap or empty space in between.

2. Now you have to tape the lens or magnifier. The lens has two faces, one smooth and the other grooved. The grooved one faces out to receive sun rays. The smooth one is on the inside of the box. Tape the lens on the inside of the box.

3. Then glue the aluminum foil on the inside of the box. This should be done on all sides except for the one on which the lens is stuck on. This is done to prevent the cardboard from burning when sun rays are directed. They will only get reflected off the aluminum pasted on each side. The shinier side of the aluminum foil should face out.

4. This gives you four surfaces inside the cardboard box. One has the lens while other three have the aluminum foil glued on. On the opposite side of the lens, cut out a square hole. The size of the hole should be about twice as that of a single marshmallow.

5. We will be roasting marshmallow through this hole. To fix the skewer, triangular tabs that bent outwards should be cut out and then the skewer should be rested on them.

6. Just puncture a marshmallow through the skewer and let it rest on the cardboard tab. Wear dark goggles and enjoy the view of a roasting marshmallow.

Frequently asked questions

What is a Fresnel lens?
Fresnel lens is a piece of plastic easily available at drug and stationary stores. It is actually used to magnify a page of a notebook and make it easier to read. Therefore, it is about the size of a notebook page. Buy one that measures seven by ten inches.

What kind of cardboard box should I use?
The box should be just the right size so that the focal length of the magnifier or Fresnel lens concentrates the sun rays. A box ten inches on each side would be perfect if the magnifier is 7 by 10. The sun rays will be centered about 10 and a half inches away from the lens.

Quick tips
To quicken the roasting and help the marshmallow absorb sun rays better, just dust cocoa powder or douse chocolate syrup on it. For well done marshmallows, hold them just at the focus point. As you move the marshmallow away from the focus, the strength of rays decreases. Instead of the skewers, you can use a hangar or fondue forks also to roast. You can also smoke sausages or barbecue chunks of meat on the skewer.

Things to watch out for
This device is susceptible to fires so don’t let children operate it in isolation even though it might look safer than roasting on an open camp fire.

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