Plastic Overmolding
Overmolding molds a second material, most often a soft-touch elastomer such as TPE or TPU, onto or around a rigid substrate that has already been molded — a soft TPU over a harder nylon is a typical pairing. It runs as two separate molding operations with two tools rather than as a 2K (two-shot) process, which Wrex does not offer. It's used for soft-touch grips, integral gaskets and seals, vibration damping, and color/material transitions on a single part.
Typical applications
- Soft-touch grips on handles and handheld product housings
- Integral gaskets and environmental seals molded directly onto a housing
- Vibration and shock damping pads on rigid enclosures
- Two-material aesthetic or ergonomic transitions on consumer and industrial parts
Process overview
- 1
Substrate molding
The rigid first-shot substrate is molded (or supplied) and inspected before overmolding.
- 2
Bond validation
We confirm chemical and mechanical compatibility between substrate and overmold resin before committing to tooling.
- 3
Overmold tooling & molding
The substrate is loaded into a second, separate tool and the overmold material is molded onto it. Wrex does not run 2K (two-shot) molding — a two-material part is two distinct molding operations with two tools, not one multi-shot tool.
- 4
Adhesion & function testing
Bond strength and function (grip, seal, damping) are verified against your requirement.
Part design considerations
- Chemical compatibility between substrate resin and overmold material — mismatched pairs won't bond reliably. A soft TPU over a harder nylon is a proven pairing we run
- Because this is two separate moldings, the substrate needs features that locate and hold it accurately in the overmold tool — design those in from the start rather than adding them later
- Overmold thickness and coverage needed for the intended function (grip, seal, damping)
- Substrate surface prep or texture where mechanical (rather than chemical) bonding is used
- Color and durometer selection for the overmold material
DFM guidance
- Confirm substrate/overmold material compatibility early — this drives resin selection more than aesthetics do
- Design in a mechanical lock (undercut, through-hole) as a backup where chemical bond alone is marginal
- Tell us the functional requirement (grip texture, IP-rated seal, damping spec) so we design the interface to meet it, not just to look right
Quality controls
- Bond/adhesion testing appropriate to the application
- Dimensional inspection of the overmolded feature
- Functional testing where the overmold is a seal (e.g., leak or IP testing) on request
Secondary operations available
- Assembly into finished product
- Pad printing on non-overmolded surfaces
- Packaging
Frequently asked questions
What materials are typically used for overmolding?
TPE and TPU are the most common overmold materials for soft-touch and sealing applications; selection depends on the substrate resin and the functional requirement. See Injection Molding Materials.
Can you overmold a substrate we supply?
Yes, with incoming inspection and a compatibility check against the intended overmold material.
Ready to talk about your project?
Send your drawings or describe your part — an engineer will follow up, not a sales queue.