Container materials must have basic heat retaining qualities. Bricks and metal containers do not work well unless they are insulated. Aluminum foil to like the inside of the box and the flaps. While it is possible to pasteurize a small amount of water without aluminum foil, its use appreciably improves performance. A dark colored solar absorber plate made of sheet metal, cardboard, or wood.
Metal works best to conduct the heat to the water containers.
A reflector to bounce in additional sunlight. If no thermometer is available, heat until bubbles are rising from the bottom steadily. Natural waxes, such as beeswax , can be used to indicate pasteurization temperature. Solar conditions, weather conditions, latitude and box efficiency are all variables that affect the ability of solar boxes to pasteurize water. Larger boxes can pasteurize more water, smaller less.