These are most widely used type of solar cookers. They can be rectangular or circular in shape. The box type of solar cooker comprises of the enclosed space where the vessel containing the raw food is kept. At the top of the box there is a glass that allows the sunrays to pass through it and get concentrated inside the box.
There are two methods of cooking the food. In first type the concentrated sunrays directly fall of the cooking vessel and cook the food. In the second method, a black surface is applied in the inner surface of box, which absorbs the sunrays and converts it into heat thus heating the food and creating a mini greenhouse effect. In either case the box is covered with the insulating material to avoid heat leaking out. It could also include a reflective surface at the top of the box instead of glass.
Althou box cookers are slow they provide even heating of the food. Box types of solar cookers are easy to make and use, safe, and cheap.