Overmoulding Services UK: When to Add Grip, Seals or Soft-Touch Features

A rigid plastic housing might protect the electronics inside it perfectly, yet still be awkward to hold with gloves. A metal handle may be strong enough for years of use but uncomfortable in the hand. Sometimes the structural material is right and it is the surface that needs to change.

That is where overmoulding can help. For UK product designers and buyers evaluating overmoulding services UK manufacturers can support, the decision is not simply whether a part would feel nicer with rubber on it. It is whether adding a second material gives the product a useful function that justifies the extra design, tooling and production work.

What is overmoulding?

Overmoulding is a manufacturing process in which one material is moulded onto or around an existing component to combine different properties in one finished part. A common example is a soft thermoplastic elastomer (TPE) grip moulded over a harder plastic handle. Suitable processes can also add resilient features to pre-made metal components.

The rigid substrate provides shape, strength and dimensional support. The overmould adds properties such as grip, cushioning, sealing or a different surface feel. Depending on the materials and design, the two layers may be held together by chemical adhesion, mechanical features or a combination. They are not automatically bonded merely because one was moulded over the other.

When should you use overmoulding?

Use overmoulding when a second material performs a clear job that the substrate cannot do well on its own, especially if integrating that feature avoids a separate assembly step. Common applications include the following.

The strongest applications solve more than an appearance problem. A single overmoulded part might improve handling while also protecting an edge from knocks. That can be valuable when repeat assembly of separate grips or seals would otherwise add work.

Grip and soft touch: more than choosing the softest rubber

Soft-touch is often used as a description of how a part feels, but the useful performance comes from the material grade, texture, coverage and thickness. A softer compound can feel comfortable yet wear too quickly or allow too much movement for a precise control. A firmer compound may be preferable on a frequently used industrial lever.

For a handheld prototype, consider the user and conditions first. Will the part be handled with bare hands or protective gloves? Will it be exposed to water, grease, cleaning products or ultraviolet light? Does a textured contact area help more than a uniformly soft coating?

The Shore hardness of an elastomer is one way to describe resistance to indentation, but it does not specify grip, durability or perceived feel on its own. A thin flexible layer over a rigid substrate can feel different from a thick pad made from the same compound. Physical samples and handling trials are valuable before tooling is finalised.

Can overmoulding create waterproof seals?

It can create an integral sealing feature, but an overmoulded elastomer does not make an assembly waterproof by default. A seal relies on controlled contact pressure, suitable material recovery, mating surface quality and consistent geometry across the assembled parts.

For a housing, the designer needs to consider the sealing lip's position, its compression when the lid closes and whether it can be damaged during assembly. Compression set, temperature exposure, fluids and repeated opening may all affect long-term performance. If a product needs a stated ingress protection rating, validate the finished assembly with appropriate testing.

The same principle applies to impact protection and electrical insulation. An overmoulded bumper may cushion knocks, but drop performance needs testing. An elastomer may be electrically insulating, but its grade, thickness and application must be assessed against the actual electrical and regulatory requirements.

Which materials can be overmoulded?

The most familiar combination is a rigid thermoplastic substrate with a softer TPE layer. Depending on grade and intended use, TPU (thermoplastic polyurethane) and TPV (thermoplastic vulcanisate) formulations may be considered for applications where abrasion, resilience or environmental resistance matter. Silicone-based systems are another option for suitable parts and processes, although their bonding and tooling requirements can differ.

Rigid substrates may include polypropylene (PP), ABS, polycarbonate (PC), PC/ABS blends and certain nylon grades. Compatibility is grade-specific. For example, an elastomer formulated to adhere to polypropylene may not bond effectively to polycarbonate. The base material and soft material should therefore be chosen as a pair, not independently from two catalogues.

Material producer Avient's technical guidance on TPE overmould selection illustrates how different elastomer families are formulated for particular substrate types. It is a useful reminder that the word TPE alone is not a complete material specification.

Overmoulding onto metal needs particular attention. A moulded elastomer may require holes, grooves, undercuts, surface preparation or a suitable bonding system to remain secure. Do not assume a dependable chemical bond to an untreated metal surface. Where failure would affect safety or performance, specify an adhesion or retention test.

Design considerations before you pay for tooling

Overmoulding works best when the second material is considered during the original part design. Adding a soft layer to a finished rigid-part design is sometimes possible, but the lack of space or retention features can force expensive changes.

Plan the interface

Identify where the elastomer starts and stops. A shallow recess can protect an exposed soft edge and help the transition look deliberate. Mechanical locks such as through-holes or undercuts may help retain the layer where suitable, although they also affect tooling complexity. Avoid relying on a thin peelable edge where the user will repeatedly catch or pull it.

Keep moulding conditions realistic

The overmould needs a flow path into its cavity, sufficient venting and a way to release the finished component from the tool. Reasonably consistent wall thickness and gradual transitions help manage filling and shrinkage. Gate position, draft, shut-off surfaces and the stability of the substrate all need review.

The substrate also has to tolerate the second moulding operation. Processing temperatures, injection pressure and shrinkage differences can distort a thin or poorly supported base part. These details are part of design for manufacture, not issues to leave until a production tool is complete.

Specify what performance means

For grip, this may involve handling trials and wear resistance. For a seal, define the intended compression and environmental conditions. For a protective bumper, identify the impacts that matter. A visual approval sample cannot establish all of these properties.

Two-shot moulding or insert overmoulding?

There is more than one way to make a multi-material component. In two-shot moulding, the first material is moulded and a second material is injected in a coordinated process using suitable multi-material equipment and tooling. This can reduce manual handling in established repeat production, but the tooling is more involved.

With a pick-and-place or insert-based approach, a rigid part is made first and then located in another tool for the overmoulding stage. That rigid part might be a moulded plastic substrate or a machined metal component. This can offer flexibility for development or smaller batches, although placing and locating the inserts introduces work and process considerations.

The correct route depends on quantity, material pairing, part geometry, available equipment and the likelihood of design changes. A metal insert project should not be assumed to use exactly the same tooling strategy as a two-plastic-component design.

When is the extra tooling cost worth it?

Overmoulding generally adds a material and a moulding operation. It may require a second tool or more complex multi-shot tooling as well as material trials and process development. For a handful of experimental components, that investment can be difficult to justify.

For repeat manufacture, however, an integrated grip or sealing feature may avoid buying, storing, positioning and attaching a separate rubber part. It may also improve consistency by reducing manual assembly steps. The value is greatest when the feature materially improves function, repeatability or handling and the design is unlikely to change frequently.

The commercial comparison should consider total delivered part cost, not just the injection moulding price. Compare the tooling investment and unit cost against alternatives such as an assembled gasket, bonded pad, separate grip sleeve or post-applied protective coating. Include assembly labour, inspection, rejects and expected volumes. There is no universal production quantity at which overmoulding automatically becomes cheaper.

How should you prototype an overmoulded product?

At an early stage, a separate grip, soft 3D printed section or cast elastomer-like sample can help assess shape and handling. These are useful for user trials, but they may not reproduce the adhesion, surface feel or durability of the intended production material.

When the bond, seal or wear properties are critical, plan a material-representative trial before approving production tooling. Attwood PD's vacuum casting, 3D printing and injection moulding support can help frame a suitable development route. The aim is to learn which features work before investing in the most committed process.

What to include in an overmoulding enquiry

Give the supplier a clear brief rather than just requesting a rubber coating. A useful starting pack includes:

• A 3D CAD model showing the substrate and intended overmould as separate bodies.
• The substrate material and proposed elastomer grade, if known.
• The function of the soft feature, including grip, sealing, wear, insulation or cushioning requirements.
• Expected production quantities, prototype timing and likelihood of design changes.
• Surface appearance, colour, texture and hardness preferences.
• Any adhesion, environmental, ingress protection or compliance tests that the finished part must pass.

This allows a manufacturer to review compatibility, tooling access, bonding strategy and whether another process might be more proportionate.

Frequently asked questions

Is overmoulding the same as insert moulding?

The terms overlap, but they are not always used in the same way. Overmoulding describes moulding one material onto another part. Insert moulding commonly refers to placing a pre-made insert, often metal, into a mould before adding plastic around it.

Will any soft TPE bond to ABS or polypropylene?

No. Bonding is dependent on the specific grades and processing conditions. Use a material pair intended for the substrate and consider mechanical retention where necessary.

Can overmoulding be used for low-volume prototypes?

It can, but dedicated tooling may not be economical for very small quantities. A staged programme using mock-ups, trials and suitable prototype tooling helps reduce the risk before production investment.

Is overmoulding better than fitting a separate gasket?

Not always. An integral seal may remove an assembly step, while a separate gasket may be cheaper to tool, easier to replace or simpler to validate. Compare the complete assembly and its service requirements.

A useful manufacturing decision

Overmoulding earns its place when the added material solves a clear problem and the overall component becomes better to use, assemble or manufacture. The right starting point is the product requirement, followed by the material pair, bond design, tooling route and test plan.

Attwood PD supports UK product development and manufacturing programmes from initial prototypes through to repeat plastic component supply. If you are considering grip, an integrated seal or a soft-touch feature, a review of the part and expected volumes can help establish whether overmoulding is the right investment.