KinexiaLEARN PHYSICS

Pizza-Box Solar Oven

No fire, no electricity — just a pizza box, some foil, and the sun. Build a working oven and cook lunch with light.

Safety:

Use oven mitts or a cloth when reaching inside — it gets genuinely hot. Do not leave the oven unattended in strong sun near flammables.

Materials

  • A clean pizza box (or similar cardboard box)
  • Aluminum foil
  • Black construction paper
  • Clear plastic wrap
  • Tape and scissors
  • A ruler and marker
  • Chocolate squares and marshmallows (for testing)

Procedure

1

Cut the reflector flap

On the box lid, draw a square about 2 cm inside the edges and cut along three sides, folding the flap up. Line the flap's underside with foil, shiny side out.

2

Blacken the base

Glue or tape black paper across the box's inside bottom — black absorbs the most sunlight and converts it to heat.

3

Seal the window

Tape plastic wrap across the lid opening to make an airtight window. This traps hot air inside like a greenhouse.

4

Load and aim at the sun

Place the chocolate and marshmallow on the black paper, close the lid, and prop the foil flap open to reflect sun through the window. Face the whole box toward the sun.

5

Cook and time it

Check every 15 minutes. Record when the chocolate first softens and when it fully melts — your oven's cooking time.

What to observe

  • The inside gets surprisingly hot to the touch within 15 minutes.

  • The chocolate melts; the marshmallow softens.

  • Angling the box toward the sun raises the temperature noticeably.

Why it happens

Sunlight streams through the plastic window and hits the black paper, which absorbs it and heats up. The box then traps that heat like a greenhouse: visible light gets in easily, but the infrared the hot interior re-radiates escapes poorly, so energy accumulates. The foil flap is a reflector that funnels extra sun inside. On a sunny day the interior passes 90 °C (194 °F) — hot enough to melt chocolate and cook a s'more, powered by nothing but radiation.

Try variations

  • Try white paper instead of black — how much slower does the chocolate melt?

  • Add a second reflector flap on the opposite side. Does cooking time drop?