How to Build a Dome Out of Foam

Updated July 20, 2017

A foam dome can be constructed easily by beginning with a foam ball. Since they vary in size from 1/2-inch diameters to 48-inch diameters, you can select the size that most closely meets your project needs. The surface texture of foam balls varies as well. You can choose a rough surface, such as the traditional styrofoam surface, or a smooth surface, such as the surface made by Smoothfoam.

Use a straight pin to secure one edge of the measuring tape to the top centre of the ball. Measure the ball from top to bottom. Divide the measurement in half to find the midpoint. Use the pencil to mark the midpoint of the ball.

Leave the straight pin holding the measuring tape in place, and rotate the measuring tape to the right. Press the measuring tape against the ball and mark the midpoint. Repeat this process, going around the entire ball and marking the midpoint. Remove the straight pin and measuring tape.

Use the electric knife to cut the ball at the marked midpoint. One half will be used for the dome, the other half is a spare piece that can be saved for another craft.

Hold one of the halves of the ball with the flat side facing up. Dip the serrated knife blade in the melted wax to allow for smoother cutting. Use the knife to hollow out the inside of the ball. Use short sawing motions and continually rotate the direction of the knife. Repeat until you have removed a satisfactory amount of foam. If the dome does not need to be hollow, this step can be omitted.


When hollowing out the dome, it may be easier to remove small chunks of foam individually rather than cutting out one big piece.


Keep the electric knife, serrated knife, and hot wax out of the reach of children.

Things You'll Need

  • Foam ball
  • Measuring tape
  • Straight pin
  • Pencil
  • Electric knife
  • Sharp serrated knife
  • Melted candle wax
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About the Author

Angela Sanzone has been professionally creating and editing business documents as a freelance writer since 2006. She previously worked as a business process analyst for a software development program. Sanzone holds an M.B.A. in management information systems and a Bachelor of Science in management, both from the University of New Orleans.