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Overmolding | Netproto

Overmolding combines materials into one better plastic part

NetProto supports custom overmolding for parts that need soft-touch grip, sealing, cushioning, impact protection, insulation, or improved product feel — from prototype validation to repeat productio

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OVermolding | Netproto

What is overmolding?

Overmolding is an injection molding process where one material is molded over another substrate to create a single integrated part. The substrate may be a rigid plastic part, metal insert, or previously molded component. The overmolded layer is often a softer material such as TPE or TPU, but it can also be another compatible rigid plastic.

  • Add soft-touch grip to rigid plastic handles, tools, covers, and handheld products.
  • Create sealing, cushioning, vibration damping, or impact-resistant features.
  • Combine color, texture, and material properties that one resin alone cannot provide.
  • Reduce separate assembly steps by integrating multiple material functions into one molded part.
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Applications | Netproto

Common overmolding applications

Overmolding is most useful when the finished product needs two material behaviors in one part.

Grip

Grip & Ergonomics

Handles, handheld tools, device housings, controllers, and consumer products that need comfort and improved grip.

Seals Cushioning

Seals & Cushioning

Overmolded gaskets, bumpers, protective edges, vibration-damping features, and impact-resistant areas.

overmold drill

Consumer product housings

Used for electronics, device housings, remote controls, and lifestyle products that need rigid structure with rubber-like zones or color contrast.

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Branding and color accents

Used when the product needs a premium visual finish, permanent color accents, texture contrast, or a molded-in brand design instead of secondary decoration.

DESIGN DECISION GUIDE | Netproto

Is Overmolding the Right Fit for Your Part?

Overmolding can improve grip, comfort, sealing, cushioning, and product feel, but it also adds material, tooling, and process considerations. Use these guidelines to quickly identify when overmolding is a strong manufacturing choice—and when your part may need extra engineering review before quoting or production.

When overmolding is a strong fit

  • The product needs both rigid support and soft-touch or flexible areas.
  • Grip, comfort, sealing, cushioning, or vibration control matters to the user.
  • The overmolded layer can be designed with clean shutoff and controlled thickness.
  • The substrate and overmold materials can bond chemically, mechanically, or through a combination of both.
  • The volume and product value justify the added tooling and process complexity.

When overmolding needs extra review

  • Material bonding is uncertain or the operating environment is harsh.
  • Thin overmold sections may create filling, flash, or durability problems.
  • The substrate may deform under second-shot pressure or temperature.
  • Cosmetic surfaces require tight control around shutoff lines and flash-sensitive edges
  • The project may be better served by assembly, insert molding, or a separate gasket depending on cost and risk.

Design guidance | Netproto

Important design considerations for overmolding

Design topicWhat to defineWhy it matters
Material compatibilitySubstrate resin, overmold resin, hardness, bond method, and operating conditions.Poor compatibility can cause peeling, weak bonding, or failure during use.
Bonding methodChemical bond, mechanical lock, undercuts, holes, ribs, or textured bonding surfaces.Bonding should not rely on hope; the geometry should support the material behavior.
Wall thicknessOvermold thickness, transitions, edge details, and flow path.Very thin or uneven sections can create short shots, sink, weak areas, or inconsistent feel.
Shutoff surfacesWhere the second material starts and stops, including flash-sensitive cosmetic edges.Good shutoff design helps control flash and creates clean material boundaries.
Substrate supportHow the first part is held in the mold during the second shot.The substrate must stay located and stable under heat, pressure, and injection force.
End-use testingPull, peel, torque, impact, chemical exposure, sealing, or grip validation grip validation. Overmolding success should be judged by final product performance, not appearance alone.

Material planning | Netproto

Common substrate and overmold material choices

Actual material selection should be confirmed through engineering review because adhesion depends on resin grade, surface condition, processing conditions, and use environment.

Common rigid substrates

  • ABS
  • PC / ABS
  • Polycarbonate
  • Nylon
  • Polypropylene
  • Acetal and engineering plastics depending on application

Common overmold layers

  • TPE / TPV / TPU soft-touch materials
  • Flexible sealing or grip materials
  • Rubber-like surfaces for comfort or damping
  • Colored or textured outer layers
  • Application-specific elastomers selected by hardness and exposure requirements

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