Silicone Molding in China: LSR vs Compression Molding

For most products sourced through silicone molding in China, the right process comes down to two things: how many parts you need, and how precise they must be. LSR (liquid silicone rubber) injection molding suits high volumes and tight tolerances — thin walls, micro-features, overmolded inserts. Compression molding suits lower volumes and simpler, thicker parts, with cheaper tooling. Transfer molding sits between the two — the usual pick for overmolding onto inserts.

Silicone molding in China is a mature, export-driven industry, and mold costs there are a fraction of Western prices. The expensive mistake is not the unit price. It is committing to the wrong process or the wrong factory before the mold is cut — because once the steel exists, you are locked in.

This is also where many buyers bring in a sourcing partner. When you need help shortlisting silicone molders, comparing DFM feedback, or verifying compliance documents, CN Ally's product sourcing team runs that process end to end.

How does silicone molding work in China?

China's silicone industry clusters around Guangdong (Dongguan, Shenzhen) and Fujian (Xiamen), where mold shops and molding plants frequently sit under one roof. The workflow is standard: you send 3D CAD files, the factory reviews them for manufacturability (DFM), the mold steel is cut, first samples (T0/T1) are produced for your approval, and then mass production begins.

Two material families dominate. Solid silicone, or high consistency rubber (HCR), is a gum-like compound processed mainly by compression or transfer molding. Liquid silicone rubber (LSR) is a two-part platinum-cured liquid processed by injection molding. Both span roughly Shore 10A (very soft) to Shore 80–90A (firm), with most consumer products between 30A and 70A. Colors are matched to Pantone references during compounding.

One practical point for buyers: ask whether the factory cuts molds in-house. A shop that machines its own tooling iterates on DFM problems in days; one that outsources it waits on a subcontractor, and you feel that delay in every sample round.

What is LSR injection molding, and when does it win?

LSR injection molding works much like plastic injection molding, but the material is a two-part liquid silicone. The two components are metered, typically at a 1:1 ratio, then mixed through a static mixer, and injected into a heated, closed mold. The part cures at roughly 120–150°C and ejects in 30 to 90 seconds, depending on thickness. The process is fully automated: sealed material lines, minimal handling, consistent cycles.

That automation is why LSR wins on precision and repeatability: published figures from Chinese molding shops commonly cite tolerances around ±0.05 mm, thin-wall capability, and flash-less molds needing little or no trimming. Because the material is platinum-cured and handled in closed systems, LSR is the default choice for food-contact and medical parts, where cleanliness and low extractables matter.

The tradeoff is tooling: precision steel, tight tolerances, and often cold-runner systems make LSR molds costlier than compression tools of similar size. The high fixed cost only pays for itself at volume, where per-unit cost drops below compression.

What is compression molding, and when is it the right call?

Compression molding is the oldest silicone process and still the most common in China for general-purpose parts. The factory cuts or weighs a preform of solid HCR silicone, places it in a heated, open mold, and the press closes under high pressure. The material flows, fills the cavity, and cures. The cycle takes several minutes rather than seconds. The operator opens the mold, removes the part, and trims the flash by hand or with simple jigs.

Where it wins is simplicity and tooling cost: a compression mold is far less complex than an LSR tool, so it is cheaper to cut and faster to modify. It handles large, thick, or simple parts well — gaskets, pads, seals, bakeware, industrial covers — and for a few hundred to a few thousand parts it is usually the cheapest route from CAD to finished goods.

The drawbacks are labor and precision: manual preform handling introduces variation, typical tolerances run around ±0.2 mm, every part carries flash that must be trimmed, and cure control is less exact: factories sometimes add a secondary post-cure to drive off volatiles and stabilize the material.

What about transfer molding?

Transfer molding is the middle path, and it deserves more attention than it usually gets. A measured charge of silicone is loaded into a transfer pot, essentially a piston-and-cylinder chamber built into the press. The piston forces the material through runners into heated mold cavities, where it cures under pressure. Typical published parameters run 2 to 12 minutes of cure time at about 260–300°F (127–150°C) and 500 to 1,000 psi. A Medical Design & Outsourcing walkthrough of the process documents the same operating window: https://www.mddionline.com/manufacturing/the-art-of-silicone-transfer-molding After ejection, parts get deflashed like compression parts.

Its real strength is overmolding onto inserts: medical instrument handles, tool grips, and electronics potted in silicone are classic transfer-molding work. It fills more complex geometry than compression while needing less tooling investment than LSR. Insert surfaces must be clean and properly prepared, though, since bond strength depends heavily on surface condition.

For medium-volume parts with inserts, quote transfer molding alongside the other two.

LSR vs compression vs transfer: how do they compare?

No single process is best — the right choice is a function of volume, precision, geometry, and budget. Here is how the three compare.

Factor · LSR injection molding · Compression molding · Transfer molding

• Material: Liquid, two-part, platinum-cured · Solid HCR preform · Solid HCR charge
• Automation: Fully automated · Manual to semi-automatic · Semi-automatic
• Cycle time: 30–90 seconds · Several minutes per shot · 2–12 minutes
• Typical tolerance: Around ±0.05 mm · Around ±0.2 mm · Between the two
• Tooling cost: High (precision steel, cold runners) · Low to moderate · Moderate
• Unit cost at scale: Lowest at high volume · Higher per part (labor) · Mid-range
• Flash and waste: Minimal (flash-less designs) · Significant flash, hand-trimmed · Moderate flash
• Best volume range: High volume · Low to medium volume · Medium volume
• Overmolding inserts: Excellent · Limited · Excellent
• Typical uses: Baby nipples, seals, wearables, medical parts · Gaskets, bakeware, pads, simple covers · Tool handles, inserts, connectors

A technical comparison from Fictiv covers the same three processes plus LSR overmolding in more depth: https://www.fictiv.com/articles/lsr-liquid-silicone-rubber-injection-molding

What do silicone molds cost and how long do they take in China?

Mold pricing varies with size, cavity count, and complexity, so treat any published figure as a starting point for quotes. Current supplier listings give a useful sense of the range: basic compression tooling commonly runs $600–800 for a simple single-cavity mold, with multi-cavity or intricate molds exceeding $1,000, while marketplace listings span from a few hundred dollars to around $2,000. LSR tooling runs higher: precision steel, tighter tolerances, and cold-runner systems push it above compression pricing for an equivalent part.

Toolmakers commonly advertise steel-mold lives in the hundreds of thousands of shots (one listing cites 100,000–500,000), which covers most buyer programs. Typical lead times run 3–6 weeks from mold design approval to finished tooling, then roughly 2–4 weeks for first samples and 4–8 weeks for mass production. Faster turnaround is sometimes advertised for urgent projects, but a compressed timeline usually means less DFM review. Not a trade you want on a first mold.

Ask for the mold steel grade in your quote (P20, H13, 718, and similar tool steels are common) and confirm who owns the mold. Standard practice in China: you paid for the tool, you own it, and you should have the right to move it to another factory.

Food-grade vs medical-grade silicone: what's the real difference?

"Food grade" and "medical grade" are not marketing tiers. They refer to different regulatory frameworks, and mixing them up can sink a product launch.

Food-grade silicone is safe for repeated food contact under FDA 21 CFR 177.2600 (US) or LFGB (the German standard widely applied in the EU). LFGB testing is stricter — it adds sensory testing (taste and odor) plus tougher extraction limits — which is why premium kitchenware and baby brands often specify LFGB even for the US market. Food-grade silicone is almost always platinum-cured, keeping it odorless and low in extractables.

Medical-grade silicone is tested for biocompatibility, most commonly against USP Class VI, and is usually produced under ISO 13485 with full batch traceability. It costs more, and competent factories run cleaner production environments with tighter documentation.

For either grade, ask for evidence before ordering: the material certificate, a third-party test report (FDA or LFGB for food contact; USP Class VI for medical), and the name of the compounding supplier. Two quick red flags: a finished part with a strong chemical smell, and a factory that cannot produce a test report matching the grade it claims.

What defects should you watch for on molded silicone parts?

Silicone is a forgiving material; molding is not. Name these defects explicitly in your QC plan.

Flash — excess material squeezed out at the parting line — is normal in compression molding and gets trimmed. Excessive flash signals worn parting lines, wrong charge weight, or insufficient clamp tonnage. LSR's flash-less molds largely eliminate it, one reason LSR unit economics improve at scale.

Flow lines are visible streaks where material fronts met during filling — caused by low pressure, wrong mold temperature, or gates forcing material through sharp thickness changes. Fixes: raise pressure, adjust mold temperature, reposition or enlarge gates.

Short shots and voids (unfilled areas, trapped air) usually trace back to inadequate venting, insufficient charge weight, or pressure problems.

Undercure shows as a tacky surface or persistent chemical smell — the part did not fully crosslink. The fix is a longer cure or post-cure bake; it is more common in compression molding, where cure control is manual.

In your acceptance criteria, specify the cosmetic standard, durometer tolerance, and cure test. Note that acceptable flash differs between compression and LSR parts, which generic checklists miss. Our quality control inspections cover this kind of process-specific checking.

Which surface finishes can you get?

Most finishes are set in the mold steel, so decide early: matte, standard polish, mirror polish, chemical textures (VDI-style), laser engraving, and silk-screen printing with silicone-compatible inks. Multi-color parts are possible through segmented molds or secondary printing.

Mirror polish costs more tooling time; texture is cheaper and hides flow lines better, which is why many consumer products use a light texture. For printed parts, confirm the ink system: ordinary inks peel off silicone.

How do you vet a silicone molder in China?

A good silicone factory is not just a building with presses. Work through this checklist before committing:

• In-house tooling. Does the factory cut its own molds, or outsource them? In-house tooling shortens every iteration.
• Process match. Confirm the factory runs the process your part needs. Plenty of shops do compression only. For LSR, ask to see the injection machines and metering setup, not just a brochure claim.
• Regulatory track record. For food or medical parts, request sample test reports carrying the factory's own name — a lab report from an unrelated company is not evidence.
• Material traceability. Can the factory trace a finished batch back to the compounding lot? For regulated products this is non-negotiable.
• Test capability. At minimum, the factory should test durometer hardness, tensile strength, and tear resistance in-house.
• References in your category. A factory that molds industrial gaskets may not be the right shop for baby products, even if the equipment looks similar.

An on-site or video audit verifying these points is cheap insurance against a bad mold investment. Our factory audit service checks tooling capability, process control, and documentation before you pay.

Frequently asked questions

What's the minimum order quantity for silicone molding in China?

Tooling is a one-off purchase, usually MOQ one. For finished parts, many factories accept small trial orders, but economical production MOQs typically run from a few hundred to a few thousand pieces. LSR needs larger runs to amortize tooling; compression can work at a few hundred pieces.

Can one factory do LSR, compression, and transfer molding?

Some larger plants run separate compression and LSR departments, but many factories specialize in one process. Do not assume a compression shop can run your LSR part: ask which machines are on the floor and request photos or video.

Is overmolding silicone onto metal or plastic inserts possible?

Yes — LSR and transfer molding both handle insert molding well: metal cores, plastic substrates, even electronics. The insert must be clean and properly prepared, and tolerances stack between insert and silicone, so DFM review matters more than for a plain part.

Platinum-cured vs peroxide-cured silicone — does it matter?

For regulated and skin-contact products, yes. Platinum-cured silicone is cleaner, odorless, and lower in extractables; peroxide-cured HCR is cheaper and fine for industrial parts but typically needs a post-cure. If a "food-grade" quote is suspiciously cheap, check which cure system the factory actually uses.

Can silicone molds handle undercuts and thin walls?

Thin walls are LSR's strength: liquid silicone fills sections solid HCR cannot. Shallow undercuts can demold without slides thanks to silicone's flexibility; deep undercuts still need collapsible cores or split molds, raising tooling cost in any process.

Do I need to specify the mold steel grade?

Specifying a known tool steel (P20, H13, 718) and target mold life keeps first-order quotes comparable. Be wary of quotes far below the rest — they may price aluminum or soft steel that wears out quickly. Put the steel grade and expected shot life in writing.

A decision rule for your first silicone order

Under a few thousand pieces a year with a thick, simple part: start with compression — cheap tooling, low risk. Tight tolerances, thin walls, inserts, or food/medical cleanliness at scale: go LSR and budget for the tooling. Inserts without LSR volume: quote transfer molding as the middle option.

Either way, the next step is the same: send 3D files and target volumes to two or three vetted factories, compare their DFM feedback — its quality tells you more than price does — and require material test reports before approving samples. To have someone run that comparison for you, write to hi@cnally.com: we shortlist silicone molders, verify process capability and compliance documents, and manage sampling until the parts are right.