Neoprene (CR) Injection Molding
Neoprene — polychloroprene — is the rubber to specify when the part has to survive weather. It resists ozone, UV, sunlight and general ageing far better than nitrile, and because of its chlorine content it is inherently flame resistant as well. What it gives up is oil resistance: neoprene handles moderate oil contact, but it is not an NBR substitute in a hydraulic or fuel seal. The choice between the two is almost always decided by a single question — does the part see oil, or does it see weather.
Specification at a glance
- Material family
- Synthetic rubber — polychloroprene, cured with metal oxides or sulfur systems
- Cure temperature
- Roughly 150–180 °C in the mould; cure time scales strongly with section thickness
- Mould temperature
- Hot — the tool cures the material rather than cooling it
- Shrinkage
- Roughly 1.5–4%, dependent on the compound, cure and section thickness
- Temperature range
- Roughly -40 °C to +120 °C
- Weather, ozone and UV resistance
- Excellent — the defining property of the material
- Flame resistance
- Good — inherently flame resistant from the chlorine content
- Oil resistance
- Moderate — adequate for incidental contact, not for hydraulic or fuel sealing
- Flex fatigue and abrasion
- Good
- Undercuts
- Practical — rubber stretches for demoulding
- Tolerances
- Wider than plastics; rubber has its own dimensioning conventions
- Molding route
- Through our vetted partner network, managed under one quality process; metal inserts machined on our own floor
- Mould tooling
- Quoted per drawing — cavity count, flash control and cure layout are reviewed before the tool is cut
- MOQ
- From 50 pieces, samples from a single piece
The weather rubber
Rubber selection usually starts with one question, and for neoprene it is this: does the part see weather?
Neoprene’s defining property is its resistance to the outdoor environment — ozone, ultraviolet light, sunlight, rain and the general ageing that follows. It is markedly better than NBR at all of them, and that is why it holds the outdoor sealing, weatherstrip, cable jacketing and mount market.
Its second distinguishing property is inherent flame resistance, from the chlorine in the polymer. Neoprene will not sustain a flame once the ignition source is removed. That is the same chemistry that makes PVC self-extinguishing, and it is why neoprene appears in cable jackets and industrial applications where a rubber part near an ignition source is a concern.
The property set:
| Property | Neoprene | NBR for comparison |
|---|---|---|
| Weather, ozone, UV | Excellent | Poor |
| Flame resistance | Good — inherent | Poor |
| Oil and fuel resistance | Moderate | Excellent |
| Temperature range | ~-40 to +120 °C | ~-40 to +100 °C |
| Flex fatigue | Good | Good |
| Abrasion | Good | Good |
| Solvent resistance | Limited | Limited |
The trade is visible in the table: neoprene gives up oil resistance to gain weather resistance. That exchange is what decides most specifications between the two materials.
NBR or neoprene: one question
The two rubbers are close enough in cost and in most mechanical properties that the choice usually comes down to the environment.
A hydraulic, fuel or oil seal → NBR. Neoprene’s moderate oil resistance is not enough for a seal that lives in hydraulic fluid; it will swell and lose its sealing force.
An outdoor seal, weatherstrip, cable jacket or mount → neoprene. NBR cracks under ozone at stressed points, and an outdoor part is generally stressed — stretched over a frame, compressed in a groove, or bent around a corner.
A part that sees both → neither is ideal. A seal on outdoor hydraulic equipment sees oil inside and weather outside, and that is a genuine specification problem rather than a simple choice. It is solved by the compound, by shielding one face, or by a different material family — and it is settled by naming both environments at the enquiry rather than by picking the rubber that sounds closer.
Rubber molding is a different process
The tool cures the material rather than cooling it, and that changes the design rules.
| Plastic injection molding | Rubber injection molding | |
|---|---|---|
| What is injected | Molten polymer | Uncured compound |
| Mould temperature | Cold relative to the melt | Hot — the tool cures the material |
| What happens in the cavity | The melt freezes into shape | The material vulcanises |
| What sets the cycle | Cooling time | Cure time, driven by heat transfer |
| Injection pressure | High | Much lower |
| Flash | A defect to avoid | A fact of the process to control |
| Tolerances | Tight | Wider, and dimensioned by their own conventions |
Cure time scales with thickness, so an uneven part is an unevenly cured part. Pressures are low, so the tool is less heavily built than a plastic tool — but rubber reaches every gap, so flash control is the dominant toolmaking concern and deflashing is a real cost.
And because rubber stretches, undercuts that would need a slider in a plastic tool can be demoulded from a simple core. That is genuine design freedom; its limit is the stretch the part can survive without tearing.
Design rules
Radius everything. Rubber tears at sharp corners. There is no yielding to redistribute the stress, so a tear simply propagates from the corner.
Avoid abrupt section changes. Blend a thickness change with a taper rather than stepping it, because a thick section cures much more slowly than a thin one.
Design for the flash line. Rubber flashes at the parting line, and on a sealing surface flash is a functional defect. The parting line position is a design decision on a seal, not a toolmaking detail.
Think about the demoulding stretch. The stretch is what limits how severe an undercut can be, and a part designed without it in mind can tear on every cycle.
Specify compression set on a long-service seal. A seal works by staying compressed against its mating surfaces, and compression set — the permanent deformation that remains after a period under compression — is what decides how long it keeps sealing. The compound and the cure both affect it, so it belongs on the specification rather than being assumed.
Specify flex fatigue on a dynamic part. Neoprene has good flex fatigue resistance, which is why it suits mounts, boots and bellows. Where a part flexes continuously, saying so allows the compound and the geometry to be chosen for it.
Agree the tolerances. Rubber dimensioning follows its own conventions, with bands that widen as dimensions grow. A drawing written to plastic tolerances will not be met by any moulder.
Molding route
Plastic and rubber molding run through our vetted partner network, managed under one quality process, while metal inserts and machined features are done on our own floor in Qidong City, Jiangsu Province, China. Tooling is quoted per drawing, and on a rubber part the review covers cavity count, flash control, cure layout and the parting line position.
Bonded rubber-to-metal parts — a metal sleeve inside a bush, a metal insert in a mount, a metal carrier bonded into a seal — are handled the same way: the insert is machined on our floor and the rubber is moulded and bonded to it by our partner, from the same drawing.
Where molding neoprene is the right choice
- Outdoor seals and gaskets on equipment that lives outside
- Weatherstrip and window seals
- Cable jackets and hose covers exposed to weather
- Vibration mounts and bushes in outdoor or wet environments — see marine and coastal parts
- Boots, gaiters and bellows where flex fatigue and weather resistance both matter
- Foam products such as padding and wetsuit material, in the appropriate grades
- Applications needing flame resistance in a general-purpose rubber
- Bonded rubber-to-metal parts where a machined insert carries the load
Where neoprene is the wrong choice
The part is a hydraulic, fuel or oil seal. Neoprene’s oil resistance is moderate, not sufficient for a seal living in oil. NBR is the material.
The service temperature is above roughly 120 °C continuously. Silicone covers a far wider range and holds compression set better at temperature.
The part meets aromatic or chlorinated solvents, ketones or esters. Those attack neoprene. It is not a general chemical barrier.
Extreme low-temperature flexibility is required. Specialty low-temperature rubbers outperform both neoprene and NBR; where a part has to stay flexible at very low temperature, that requirement decides the material.
A standard catalogue part would work. Buying a standard gasket or seal is cheaper than tooling a custom one — a moulded custom part should exist because the geometry demands it.
What to put on the drawing
| Instead of | Write |
|---|---|
| Rubber | Neoprene (CR), for an outdoor or weather-exposed part |
| Neoprene, oil or fuel contact | Wrong material for a seal — NBR is the oil-resistant rubber |
| Neoprene, service temperature | State both ends — the compound is chosen for the balance |
| Neoprene, long-service seal | Specify compression set — it decides seal life |
| Neoprene, dynamic part | Specify flex fatigue resistance |
| Neoprene, sealing surface | Say which surface seals — the flash line must avoid it |
| Neoprene, tolerance | Agree it — rubber tolerances are wider than plastics |
| Neoprene, meets solvents | Name the chemical — neoprene has limited solvent resistance |
The three lines that decide most neoprene mouldings are whether the part sees weather or oil, the temperature range, and which surface has to seal. The first is the deciding factor between neoprene and NBR. The second picks the compound. The third decides the parting line, and on a seal that is a functional requirement.
Send the drawing through the request a quote form and the reply comes back within 24 hours with DFM feedback — including a note on the compound, the cure, the compression set requirement and the parting line where any of them need settling.
Rubber and plastic parts rarely sit alone in an assembly: they are clamped, located or retained by a fastener. When that fastener has to be made to a drawing rather than bought from a catalogue, the same rules apply as for any turned part — a thread class, a locating diameter with a stated tolerance, and a quantity that justifies a setup. The metal side of that pairing is covered under custom screws.
Frequently asked
- What is neoprene injection molding used for?
- Outdoor and weather-exposed rubber parts: seals and gaskets on outdoor equipment, weatherstrip and window seals, cable jackets, hose covers, vibration mounts and bushes, boots and gaiters, bellows, footwear components, and foam products such as wetsuits and padding. Anywhere a flexible part has to survive sunlight, rain, ozone and temperature cycling for years.
- What is the difference between neoprene and NBR?
- The environment each one is built for. NBR has outstanding oil, fuel and hydraulic fluid resistance but poor weather and ozone resistance. Neoprene has outstanding weather, ozone and UV resistance but only moderate oil resistance. So the deciding question is usually simple: does the part see oil, or does it see weather? Hydraulic and fuel seals go to NBR; outdoor seals, weatherstrip and cable jackets go to neoprene. Where a part sees both, neither is ideal and the compound or the material family has to be reconsidered.
- Is neoprene flame resistant?
- It is inherently flame resistant, because of the chlorine in the polymer — the same chemistry that makes PVC self-extinguishing. Neoprene will not sustain a flame once the ignition source is removed, which is one of the reasons it appears in cable jackets, in mining and industrial applications, and in any service where a rubber part near a potential ignition source is a concern. NBR has none of this property, so where flame behaviour matters, neoprene is the general-purpose rubber to choose.
- What is neoprene's temperature range?
- Roughly -40 °C to +120 °C, which is slightly wider than NBR's at the top end. As with any rubber the exact range depends on the compound: grades formulated for better heat resistance give up some low-temperature flexibility, and vice versa. Where a part has to work across a wide range, the compound is chosen for the balance the application needs rather than assumed from a generic figure.
- How is rubber injection molding different from plastic injection molding?
- The tool cures the material instead of cooling it. An uncured compound is injected into a heated mould, where it vulcanises — cross-links — in the cavity. Cure time is driven by heat transfer into the part, so a thick section takes much longer to cure than a thin one, and an uneven part is an unevenly cured part. Injection pressures are much lower than for plastics, so the tool is generally less heavily built, but rubber flows into every gap, so flash control matters more and deflashing is a real cost.
- Why can rubber parts have undercuts?
- Because rubber stretches. A rigid plastic part with an undercut needs a slider, a lifter or a collapsing core in the tool, because the part cannot deform enough to release. A rubber part can be stretched off a simple core, so a form that would be impossible in plastic is straightforward in rubber. That is genuine design freedom, and it is why rubber parts often have shapes that look unmouldable. The limit is the demoulding stretch the part can survive without tearing.
- What tolerances can a moulded neoprene part hold?
- Wider than a plastic part, and the difference surprises buyers who are used to plastics. Rubber shrinkage is larger and less predictable — it depends on the compound, the cure cycle and the section thickness — and the material is flexible, so it deforms under measurement. Rubber dimensioning follows its own conventions, with tolerance bands that widen as the dimension grows. Tolerances are agreed per drawing in DFM rather than carried over from a plastic part.
- What design rules matter for a moulded rubber part?
- Radius everything, because rubber tears at sharp corners. Avoid abrupt changes in section thickness, because they cure unevenly. Design for the flash line — rubber flashes at the parting line, and on a sealing surface flash is a functional defect rather than a cosmetic one. And think about how the part will be stretched off the core, because that limits how severe an undercut can be. For a dynamic part, compression set and flex fatigue both belong on the specification.
- Can neoprene be bonded to metal?
- Yes, and bonded rubber-to-metal parts are common in this material — a metal sleeve inside a bush, a metal insert in a mount, a metal carrier bonded into a seal. The inserts are machined on our own floor and the rubber is moulded and bonded to them by our partner, from the same drawing, so the fit between rubber and metal is planned before the tool is cut.
- Does neoprene resist chemicals?
- It handles moderate oil contact, water, weathering, ozone and many dilute chemicals, and it is better than NBR against some acids and bases. It is not a general chemical barrier, and it is attacked by aromatic and chlorinated solvents, ketones and esters. Where a part meets a specific chemical, name it — 'chemical resistance' without a named chemical is a specification by hope rather than a decision.
Related pages
Other Rubber & Silicone materials
Have a part in Neoprene (CR)?
Send the drawing, the grade and the quantity. You get DFM feedback and a price within 24 hours, and orders start at 50 pieces per style and material.