Insert Molding vs Over Molding: What's the Difference?
Insert molding places a solid component (often metal) into the mold and encapsulates it with plastic. Over molding molds one material over another already-molded substrate — usually a soft thermoplastic elastomer over a rigid plastic. In short: insert molding integrates dissimilar materials like metal and plastic, while over molding bonds materials for grip, sealing or appearance.
What is insert molding?
Insert molding encapsulates a pre-placed insert — a threaded bush, terminal or pin — in a single injection shot, producing a strong, assembly-ready part. Read our full guide to insert molding.
What is over molding?
Over molding is a multi-material process in which a second material is molded over a first, already-molded part — for example a soft TPE grip over a rigid nylon handle — bonding the two into one component.
Insert molding vs over molding at a glance
| Insert Molding | Over Molding | |
|---|---|---|
| Definition | Plastic molded around a pre-placed insert | One material molded over another molded part |
| Typical materials | Metal insert + engineering plastic | Rigid plastic + soft TPE/TPU |
| Primary purpose | Strength, threads, metal-plastic integration | Grip, sealing, ergonomics, aesthetics |
| Common uses | Connectors, threaded parts, terminals | Handles, seals, soft-touch buttons |
| Process | Single shot around insert | Two shots / two materials |
| Bonding | Mechanical encapsulation | Chemical/mechanical bond between plastics |
When to choose insert molding
- You need durable metal threads or contacts
- You want to combine metal and plastic in one part
- You need to reduce fasteners and assembly steps
When to choose over molding
- You need a soft-touch grip or ergonomic surface
- You need sealing, gasketing or vibration damping
- You want multi-colour or multi-material aesthetics
Frequently Asked Questions
Can insert molding and over molding be combined?
Yes. A part can use an insert (e.g. a metal terminal) and also be over molded with a soft material, depending on design requirements.
Which is more expensive, insert or over molding?
It depends on the part. Over molding usually needs two shots/materials; insert molding needs insert placement. Rollex can advise the most cost-effective route for your part.
Does Rollex offer both processes?
Yes — Rollex Industries provides both insert molding and over molding from its facilities in Pune, India.
Not sure which process fits your part?
Send us your design and we'll recommend insert molding, over molding, or a combination.
Contact Rollex Industries