Overmolding vs Insert Molding: Differences & Applications

Mr. Liu· Engineering DirectorJuly 11, 2026

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.

overmolded / multi-material plastic part

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?

Insert molding molds plastic around a pre-placed insert (usually metal, like a threaded bushing). Overmolding molds a second material over an existing molded plastic part (like a soft grip over a rigid handle). Insert molding adds a non-plastic component; overmolding adds a second plastic/elastomer layer.

Is overmolding a two-shot process?

Usually. The rigid substrate is molded first, then the second material is overmolded onto it — either in a two-shot machine or by transferring the substrate to a second mold. Some simple overmolds place a pre-made substrate as an insert.

What materials are used for overmolding?

A rigid substrate (e.g. ABS, PC, nylon or PP) with a softer overmold such as TPE or TPU for grips and seals. The substrate and overmold must be chemically compatible so they bond; suppliers publish bonding compatibility charts.

Why use insert molding instead of assembling afterward?

Insert molding locks metal features (threads, contacts, pins) into the plastic in one shot — stronger and more precise than press-fitting or gluing later, and it removes a secondary assembly step and its cost.

Can you overmold onto metal?

Yes — overmolding (or insert molding) can encapsulate metal parts with plastic or elastomer, e.g. for grips, strain relief on cables, or sealing around a metal component.

Sources & further reading: MatWeb — polymer & elastomer properties · ISO 2768 general tolerances.

Explore how Sendot Technology can manufacture your custom parts: