Not sure which process your part needs? That's the first conversation.
Send the print — the recommendation comes out of DFM, with the reasoning attached.
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Liquid injection molding (LSR), compression rubber molding, transfer molding, overmolding / insert molding, gum molding, and flashless molding — the full elastomer range under one roof and one ISO 13485:2016 quality system. So your part's geometry, material, tolerance, and volume curve choose the process, and the process is justified to you. Not the other way around.
When a shop runs nothing but compression rubber molding, every part comes back as a compression rubber part. When a shop only does high-volume LSR, your clinical-stage build isn't worth their changeover. Either way, the design bends to the machine — tolerances loosen, geometry simplifies, or the program waits.
We run the decision the right direction. Because liquid injection molding, compression rubber molding, transfer molding, overmolding / insert molding, gum molding, and flashless molding all live on one floor, no geometry gets forced into the wrong process — and every process recommendation comes with the reasoning attached.
The process is selected around the part — its geometry, material, tolerance, and volume curve — not around whichever press a supplier happens to own.
Before any process is quoted, the part gets a design for manufacturability review: technical sessions where IRP engineers deep-dive the design, flag what will and won't mold, and recommend the adjustments that let the part be made the way it was intended. The process recommendation below is an output of that review — the full engineering engagement, from DFM through validation, lives on Engineering & Manufacturing →
| Process | Typical materials | Geometry suited to | Tolerance range | Typical volumes | Cleanroom availability |
|---|---|---|---|---|---|
| Liquid injection molding (LSR) | Liquid silicone rubber (LSR) | Small, complex, high-cavitation parts; thin walls and fine detail; full automation | [VERIFY] | [VERIFY] | ISO Class 8 cleanroom environment molding |
| Compression rubber molding | Organic & synthetic rubber compounds; HCR silicone | Larger parts and simpler cross-sections; economical tooling | [VERIFY] | [VERIFY] | [VERIFY] |
| Transfer molding | HCR silicone; rubber compounds | Multi-cavity dimensional control; molding around inserts | [VERIFY] | [VERIFY] | [VERIFY] |
| Overmolding / insert molding | Silicone or rubber over plastic substrates and metal inserts | Bonded multi-material parts — silicone permanently joined to a substrate the part can't function without | [VERIFY] | [VERIFY] | [VERIFY] |
| Gum molding | Gum-stock silicone (HCR) | Properties, sizes, and durometers outside LSR's window | [VERIFY] | [VERIFY] | [VERIFY] |
| Flashless molding | Tooling approach applied across silicone and rubber molding | Zero-flash sealing surfaces; components in the drug or fluid path | [VERIFY] | [VERIFY] | [VERIFY] |
Most programs don't arrive knowing the answer. That's the point of the engineering engagement: the process recommendation comes out of DFM, not off a brochure.
Medical programs need small, complex, biocompatible silicone components held to tight tolerances at production volumes — with zero flash and zero contamination.
Two-part liquid silicone rubber is metered, mixed, and injected into heated precision tooling, curing in seconds — the most automatable and repeatable process in medical silicone, and our core discipline since 1980. Late-model LIM presses, hot and cold runner tooling, fully automated work cells, ISO Class 8 cleanroom environment molding, 24/7 when programs demand it. The proof runs on video: a 128-cavity cold runner mold, demolded by robot sweep.
Liquid Injection Molding →Rubber is not injection molded — rubber compounds cure in the mold under heat and pressure. When your part is specified in an organic or synthetic rubber, this is where it gets made.
Compression rubber molding also carries larger silicone parts and leaner volumes where injection tooling isn't justified: lower tooling investment, efficient production, the same quality system.
Compression Rubber Molding →Some parts need tighter dimensional control than compression rubber molding gives — or need material molded around an insert without shifting it.
In transfer molding, material moves from a pot into closed cavities under pressure: tighter multi-cavity control, and a natural fit for molding around inserts — for silicone and rubber compounds alike.
Transfer Molding →Devices need silicone permanently bonded to something that isn't silicone — and coordinating a molding supplier, an adhesive process, and a bonding vendor multiplies the ways a bond can fail.
The two names describe two substrates. Overmolding is silicone molded onto a plastic substrate. Insert molding is silicone molded onto a metal insert. Different substrates, sometimes different device teams — one discipline: substrate preparation, bond validation, and molding around a component without damaging or displacing it.
Every overmolded or insert-molded part leaves IRP as a bonded, validated sub-assembly from one supplier under one ISO 13485:2016 quality system. For rubber-over-plastic parts we mold the thermoplastic substrate too, so both halves of the bond carry one accountable name. Substrates run from plastics and metals to fabric and other silicones.
Overmolding / Insert Molding →Some parts need properties, sizes, or hardnesses outside LSR's window.
Gum molding processes high-consistency gum-stock silicone (HCR), opening a wider property and durometer range than liquid silicone — while keeping the part in the same facility and quality system as everything else on this page.
Gum Molding →In a medical component, flash isn't cosmetic. It's a contamination path and a function risk — especially where the part meets the drug or fluid path.
Flashless tooling engineers the flash out at the tool rather than trimming it off afterward: no deflash handling, no particulate introduced, nothing for inspection to catch downstream.
Flashless Molding →Silicone reads like rubber, but it isn't rubber — it's an elastomer, and it behaves like one. Most programs arrive with the material already selected. IRP's job is to confirm that the material, the process, and the geometry agree — and to support the choice where it's still open.
| Material family | Typically specified for | How IRP supports the selection |
|---|---|---|
| Liquid silicone rubber (LSR) | Biocompatible, thermally stable, precise — the default for high-volume medical molding | Supplier-agnostic sourcing across the major LSR manufacturers — the spec picks the material, not a supply agreement |
| High-consistency rubber (HCR) | Properties, sizes, and durometers outside LSR's window | Processed by gum molding, compression rubber molding, and transfer molding — the process follows the grade |
| EPDM | Steam, hot-water, and polar-chemistry resistance where silicone isn't the fit — a workhorse non-silicone elastomer for seals and gaskets | Compounded to spec and molded by compression rubber molding and transfer molding |
| Fluorosilicone | Silicone performance plus resistance to fuels, oils, solvents, and aggressive chemistry | Selection and validation support against the application environment |
| Rubber compounds (organic & synthetic) | Applications that call for a non-silicone elastomer | Molded by compression rubber molding and transfer molding, under the same quality system as the silicone work |
Where the application demands biocompatibility, selection support covers medical-grade and USP Class VI-rated materials and the documentation behind them — so the material you validate is the material you can defend.
And where the right compound doesn't exist on a shelf, IRP develops it: custom elastomer formulation to spec — including one proprietary compound of our own, recommended where it genuinely fits. Your specification still leads; material development is in service of it, never a substitute for it.
Everything on this page — every process, every material family — runs under one ISO 13485:2016-certified quality system in an FDA-registered facility in San Clemente, CA. Choosing a different process never means changing suppliers, re-auditing a facility, or splitting a program across quality systems.
IRP makes custom medical components and bonded sub-assemblies — the molded elastomer parts inside your device, and the secondary operations, tooling, and silicone extrusion that surround them. What IRP is not is a contract manufacturer — and the lines are drawn deliberately:
The component design is yours. IRP contributes design for manufacturability and mold design — the recommendations that make your part moldable, and the tooling engineered to mold it.
Thermoplastics appear in service of the elastomer — molded substrates for overmolding / insert molding, so both halves of a bonded part come from one supplier. If your program pairs extruded thermoplastic with the elastomer, bring it into the same conversation.
IRP builds the components that go into your device, not the device. Final device assembly belongs with a contract manufacturer — the parts they assemble are where IRP fits.
The narrow claim set is deliberate. Everything on this page is something the floor actually runs — and every step IRP does absorb, from molding through secondary operations, is one less supplier for your team to source, qualify, and manage.
The names describe two substrates. Overmolding is silicone molded onto a plastic substrate; insert molding is silicone molded onto a metal insert. The discipline is the same — substrate preparation, bond validation, and molding around a component without damaging or displacing it. IRP runs both, and for rubber-over-plastic parts can mold the thermoplastic substrate as well, so both halves of the bond come from one supplier.
When the material or the economics say so. Rubber compounds are not injection molded — rubber is compression molded — so a part specified in an organic or synthetic rubber runs as compression rubber molding. It is also the right call for larger silicone parts and leaner volumes where injection tooling isn't justified. IRP's engineers make that call during DFM review, with the reasoning attached.
Yes. Silicone and rubber are both elastomers, and IRP molds both: silicone by liquid injection molding, gum molding, and transfer molding, and organic and synthetic rubber compounds by compression rubber molding and transfer molding — all under the same ISO 13485:2016 quality system.
Most programs arrive with the material already selected, and that's the expected starting point. IRP confirms the selection — that the material, the process, and the part's geometry agree, and that biocompatibility requirements such as USP Class VI are covered — and supports the choice where it's still open, across LSR, HCR, EPDM, fluorosilicone, and rubber compounds. Where the right compound doesn't exist off the shelf, IRP develops it: custom elastomer formulation to spec.
It depends on the part — what IRP holds is a function of geometry, material, and process, and a single blanket number would be misleading. Send the print: IRP's engineers review it and confirm what the part's critical dimensions can hold in the recommended process.
Send the print — the recommendation comes out of DFM, with the reasoning attached.