Overmolding vs Insert Molding: Differences & Applications
Insert molding molds plastic around a pre-placed insert (usually a metal part like a threaded bushing or terminal). Overmolding molds a second material over an already-molded plastic part (typically a soft TPE grip over a rigid base). Both create a single integrated part in the mold — insert molding adds a non-plastic component; overmolding adds a second plastic layer.
See our rapid tooling & injection molding service, and the guide to overmolding.
Key takeaways
- Insert molding = plastic molded around a pre-placed insert (metal threads, pins, terminals) — one shot.
- Overmolding = a second material molded over an existing molded part (e.g. soft-touch grip over rigid handle) — usually two shots.
- Both eliminate assembly and glue, creating a strong, integrated part.
- Overmolding needs material compatibility (bonding) between substrate and overmold; insert molding needs the insert located and retained.
- Have a multi-material part? Get a quote and DFM review.
Insert molding vs overmolding — comparison
| Attribute | Insert molding | Overmolding |
|---|---|---|
| What's added | A pre-made insert (often metal) | A second molded material (usually plastic/TPE) |
| Process | One shot around the placed insert | Usually two shots (substrate, then overmold) |
| Typical use | Threaded bushings, terminals, pins in plastic | Soft grips, seals, 2-color parts |
| Key requirement | Insert located & retained in the mold | Material bond compatibility |
| Benefit | Strong metal-in-plastic features, no post-assembly | Ergonomics, sealing, aesthetics in one part |
Insert molding
In insert molding, a pre-made component — most often a metal insert such as a threaded bushing, pin, terminal or stud — is placed into the mold, and molten plastic is injected around it to lock it in place. The result is a single part with strong, precise metal features (threads that won't strip, electrical contacts, load-bearing bosses) without any secondary assembly. The insert must be accurately located and retained so it doesn't shift during injection.
Overmolding
Overmolding molds a second material over an existing (already-molded) substrate. The classic example is a soft thermoplastic elastomer (TPE) grip molded over a rigid plastic handle for comfort and grip; it's also used for seals, 2-color parts and protective layers. It's usually a two-shot process (mold the substrate, then the overmold), and the two materials must be chemically compatible so the overmold bonds to the substrate. See overmolding principles & methods.
How to choose
- Need metal features (threads, contacts) in a plastic part: insert molding.
- Need a soft grip, seal, or second color/material: overmolding.
- Replacing an assembly + fasteners/glue: either — both integrate parts and cut assembly.
Applications
- Insert molding: electronics (terminals/contacts), threaded inserts, automotive connectors, medical devices.
- Overmolding: tool & toothbrush handles, seals/gaskets, wearables, 2-color consumer products.
Frequently asked questions
What is the difference between insert molding and overmolding?
Is overmolding a two-shot process?
What materials are used for overmolding?
Why use insert molding instead of assembling afterward?
Can you overmold onto metal?
Sources & further reading: MatWeb — polymer & elastomer properties · ISO 2768 general tolerances.
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