Bouncing Custard Balls

How to make custard bounce. Follow this simple guide to make bouncy custard balls, and find out the science behind it.



  • Non-latex gloves
    (for children with eczema/sensitive skin/open cuts)
  • Lab coats
  • Safety glasses
  • Disposable plastic cups
  • PVA Glue (Craft Planet is best)
  • 4% Borax Solution
  • Custard Powder
  • Tablespoons
  • Teaspoons
  • Pipette
  • Wooden tongue depressors


  1. Pour 1 x tablespoon (2 lines from bottom of cup) of PVA glue into a plastic cup
  2. Add 1 tsp of custard powder to the PVA glue and mix using a wooden tongue depressor
  3. Add 4mls of borax solution to the glue mixture. Stir thoroughly until your mixture stiffens – you will have to spend a few minutes doing this
  4. Knead/rub the mixture using your hands until it becomes elastic, stuck-together and drier. Shape the material into a ball and check how well it bounces
  5. If it’s too dry, it needs more water. If it’s too wet, it needs more custard powder

The Science

A chemical reaction takes place. The borax cross-links two polymers (long-chain molecules) i.e. cornflour (contained in the custard powder) and PVA glue.


Health and Safety

Powdered Borax may be a risk to pregnant women. Please check online material hazard sheets for Borax prior to its use. Borax can be an irritant in liquid form so please ensure any children with sensitive skin are wearing gloves. To protect clothing and eyes from splashes, please ensure all children are wearing lab coats and safety glasses.