How to Build a Milk Carton Car

Many Balloons image by Vanessa van Rensburg from

Things You'll Need

  • Clean, dry, half-gallon milk or juice carton
  • Four large bottle caps
  • Straws
  • Glue
  • Party balloon
  • Pencil

Hands-on science activities satisfy a young child’s natural curiosities. Hands-on science activities teach problem-solving skills. Create teams and make up competition rules like: No more than two balloons can power a car. Teams may make more than one car. Each team gets two tries to make cars go 15 feet. Break ties by a face-off race (one try for each team). This experiment encourages children to keep trying and experimenting until it works.

Obtain a quart milk or juice carton for the body of the car. Wash out the milk carton with liquid dish soap.

Cut the carton in half lengthwise. Designate the pour spout as the front of the car.

Punch a small hole into the middle of the back end of the car. This hole is for the open end of the balloon to pass. Start with a small hole, but make it bigger if it does not let enough air escape.

Punch four holes in the sides of the carton with a pencil. Punch two pencil holes in the front and two pencil holes in the back of the balloon car. Create these holes near the bottom of the milk carton to hold the axles.

Cut four evenly spaced 1/4-inch slits in each end of the straws. Insert the straws through the four holes of the car.

Fold the slit sections of the straw ends backward to make tabs. Glue the straw tabs onto the flat tops of the four plastic caps to form wheels. Be sure to center the tabs on the caps.

Inflate the balloon fully, but do not tie it closed. Let go. The balloon car will zip around the room until deflated. When air rushes out, it pushes at the balloon with an equal force in the opposite direction. The car becomes gas-powered.


  • Decorate the new car with tempera paint on the outside surface. Put in a drop or two of liquid dish soap; this allows the paint to stick to the waxy carton coating.