How to mold plastic

Updated July 20, 2017

Shaping your own plastic objects using a mould means purchasing two kits from your local hobby store. One is a plastic resin kit, and the other is a kit of mould-making putty. The principle behind both kits is very similar. You can create both your mould and the plastic for your casting by mixing the components of the kits together. Doing so starts a chemical reaction that begins to harden into the final product

Set down newspaper over your work space. Choose a work space with a lot of ventilation, as the fumes from the liquid plastic are not good for you. Put on a face mask and a pair of nitrile gloves.

Set your prototype object on top of the newspaper and retrieve the two tubes of mould-making putty from your kit. Each tube contains a differently coloured putty. Tear off equal chunks of each, enough to potentially cover your prototype.

Knead the two lumps of putty together until the mixture becomes a streak-free uniform colour. Place the blob of mixed putty on top of your object and drag the putty over the prototype with your fingers until it is completely covered. Press your fingers into the putty at any spot where there is an undercut or a significant amount of detail. This will ensure that the putty picks it up.

Wait between 5 and 20 minutes for the putty to harden into flexible silicone rubber. You can test the putty by pinching it between your fingers. If it springs back into its original form, it has hardened. Remove the prototype from the newly made rubbery mould.

Set out a pair of mixing cups and label them A and B. Retrieve the two bottles of fluid from your plastic resin kit. These bottles contain the plastic and its catalyst. Pour an equal amount of each bottle into the two separate cups, enough to potentially fill your mould.

Pour the contents of the two cups together into a third cup and stir the mixture for one minute with a craft stick. Then pour the mixture into your mould.

Let the plastic harden at least an hour. Some plastics harden in minutes, others take much longer. Consult your kit's instructions for an accurate measurement. When the plastic has hardened, simply pop it out of your mould.


Keep the uncured plastic away from children and animals.

Things You'll Need

  • Newspaper
  • Face mask
  • Nitrile gloves
  • Prototype
  • Mold putty kit
  • Mixing cups
  • Plastic resin casting kit
  • Popsicle stick
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About the Author

Jennifer Meyer received her B.A. in anthropology, specializing in archeology, in 2004 from Beloit College. She then earned her master's degree in museum studies at Indiana University in 2007 after being awarded a university fellowship. She started writing in 2005, contributing podcast scripts, procedural guides and exhibit copy to museums in the Indianapolis metro area.