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Overmolding is a process where a single part is created using two or more different materials in combination.

About Overmolding

  • Rubber-like TPEs/TPVs on the exterior of plastic parts can help the piece resist water or absorb sound. The TPE/TPV layer can also serve as electrical insulation.
  • Overmolding can help keep dust and water out of plastic components, making them last longer.
  • Overmolding can help add a second layer that can make grips more comfortable on any parts that people hold or grasp.

Advantages of Overmolding

  • Reduced assembly and labor costs (Molded as one integrated part)
  • Eliminates bonding step in the manufacturing process
  • Improved part strength and structure(e.g, rubber exterior absorbs impact)
Accuracy & Efficiency
  • In higher volumes, molded parts preserve a higher precision and less waste than other manufacturing processes.
  • Custom plastic overmolding allows for production of parts molded of multiple thermoplastic materials
Surface Quality
  • Improve the looking and feeling with combination of different colors and hardness.


There are a lot of reasons to overmold. Among the most common are the following:

  • As a means to break up the color (aesthetic impacts).

  • To provide a soft grip surface around a part of a separate material.

  • To add flexible areas to a rigid part.

  • To eliminate assembly line time. Instead of manufacturing a metal tool and a plastic handgrip separately and then joining the two together manually or with automation, you can just overmold the metal tool with a plastic handgrip and eliminate the need for assembly altogether.

  • To capture one part inside of another without having to use fasteners or adhesives.

Overview: What is Overmolding?

What is Overmolding?

With overmolding, the production of the substrate parts is a standard injection molding process involving an aluminum mold with no heating or cooling lines running through it. Cycle times are a bit longer, which allows our molders to monitor fill pressure, cosmetic concerns, and the basic quality of the parts. When the total run of substrate parts are molded, overmold tooling is then assembled to the press. The substrate parts are placed by hand into a mold where each part is overmolded with either a thermoplastic or liquid silicone rubber material.

How does Overmolding Work?

Simply put, overmolding lets you combine multiple materials into one part. One material, usually a thermoplastic elastomer (TPE/TPV), is molded onto a second material, which is often a rigid plastic. Think about your toothbrush handle where the single piece has both rigid and rubbery components. It’s a great way to make plastic parts perform and look better.

Overmolding Design Tips:

  • Wall thicknesses between 0.060″ to 0.120″ (1.5 mm-3 mm) generally provide the best bonding.
  • Keeping radii between 0.020″ or 0.5mm minimum in corners reduces localized stresses.
  • If the part requires the use of thick TPE sections, they should be cored out to minimize shrinkage problems, reduce the part weight, and lower cycle time.
  • Avoid deep or un-veritable blind pockets or ribs in your design.
  • Use gradual transitions between wall thickness to reduce or avoid problems with the flow (backfills, gas traps, etc.)
  • The TPE/TPV should be less thick than the substrate to prevent the warpage, especially if the part is flat, long, or both.
  • Overmolding needs mechanical or chemical bonding to the substrate, so your material choices should enable this.

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