Views: 0 Author: Peter Cui Publish Time: 2026-05-29 Origin: Mitour Silicone
Table of Contents
TL;DR — Liquid Silicone Rubber (LSR) injection molding and High Temperature Vulcanization (HTV) compression molding are the two dominant silicone manufacturing processes. LSR offers tighter tolerances, faster cycle times, and is preferred for baby-contact and medical applications. HTV costs 40–60% less per mold and handles larger parts more economically. At Mitour Silicone's 4,500 m² Shenzhen facility, we run 20+ LSR injection machines alongside HTV compression lines — and choosing the wrong process for your product is the most expensive mistake a buyer can make.
LSR (Liquid Silicone Rubber): two-part platinum-cure liquid compound injected under pressure, cures in 15–45 seconds, ideal for tight tolerances and baby/medical applications.
HTV (High Temperature Vulcanization): solid rubber compound pressed in an open mold under heat, cycle time 3–8 minutes, ideal for larger, lower-complexity parts and cost-sensitive runs.
Mold cost: LSR molds run 2–3× the cost of equivalent HTV molds due to tighter shutoff requirements and cold runner systems.
Cycle time: LSR is 4–10× faster per cavity, which offsets mold cost at medium-to-high volumes.
Material purity: both can achieve FDA 21 CFR 177.2600 compliance, but LSR's closed system is less susceptible to environmental contamination during processing.
Shore A hardness range: LSR 10–80; HTV 20–80. Softest parts (Shore A 10–25) almost always require LSR.
When in doubt: ask whether flash is acceptable in your design. LSR produces near-zero flash; HTV always produces some.
To make sense of the manufacturing differences, you need a 90-second chemistry lesson. Both LSR and HTV are silicone elastomers — polymer chains of alternating silicon and oxygen atoms (Si-O backbone) with organic side groups. Their differences come from how they crosslink (vulcanize) and in what physical state they start the process.
LSR chemistry. LSR is a two-part system: Part A contains the silicone polymer and a platinum catalyst; Part B contains the crosslinker (typically a vinyl-terminated silicone). Mix them at the metering unit in a 1:1 ratio, inject into a hot mold (150–200°C), and platinum-catalyzed hydrosilylation crosslinks the chains in 15–45 seconds. No by-products. The result is a consistent, highly pure elastomer.
HTV chemistry. HTV starts as a solid gum — a very high molecular weight silicone polymer on a silica filler base. It becomes processable only when mixed with a peroxide or platinum crosslinker on a two-roll mill. The milled compound is sheeted, cut into preforms, placed in an open mold, pressed under 100–200 bar, and cured at 160–200°C for 3–8 minutes. Peroxide-cured HTV releases acetic acid or other by-products; platinum-cured HTV does not. Post-curing in an oven (200°C for 4 hours) drives off residual by-products and stabilizes properties.
This chemistry distinction matters because LSR's closed injection system is inherently cleaner. There is no operator handling compound at an open mill; no preform cutting on a bench; no ambient particulate exposure between milling and pressing. For baby nipples, pacifiers, and medical components where bioburden is a concern, that matters.
An LSR injection molding cell consists of a metering and mixing unit (MMU), an injection molding press (typically 50–400 ton clamp force for silicone parts), and a cold-runner mold system. The MMU feeds two-part LSR at precise 1:1 ratio — ratio error of even 2% degrades cure uniformity — into the cold-runner manifold, which keeps the material at 5–10°C to prevent premature crosslinking. The mold itself is heated to 170–200°C. Material enters cold, hits the hot mold surface, and cures almost instantaneously.
At Mitour Silicone, our 20+ LSR injection machines run parts from 0.5 g (pacifier nipples) to 800 g (large silicone collapsible containers). Clamp force ranges from 80 to 320 tons. All machines run under positive-pressure cleanroom-adjacent conditions for baby and food-contact products.
LSR mold design is substantially more demanding than HTV. The key constraints:
Shutoff precision. Flash in LSR is function of mold parting-line clearance. LSR at injection pressure (10–60 MPa) has extremely low viscosity (similar to motor oil) and will penetrate gaps under 0.01 mm. Mitour Silicone specifies shutoff tolerances of 0.005 mm for baby-contact molds. This demands hardened steel (typically 1.2343/H11 steel, HRC 48–52) and precision EDM finishing.
Cold runner systems. Without a cold runner, every shot wastes material in a hot sprue, which also requires operator removal. Our cold runner tools eliminate sprue waste and reduce cycle contamination. Cold runner systems add USD 1,500–4,000 to mold cost but recover that investment rapidly in material savings and cycle efficiency at volumes above 10,000 units.
Self-venting molds. LSR cures so fast that air evacuation during injection is critical. Our molds incorporate laser-cut micro-vents (0.002–0.005 mm wide) that allow air to escape without allowing LSR to flash through. This is the detail most buyers never see but that separates a well-run LSR operation from one that produces parts with air voids or surface dimples.
A four-cavity LSR mold on our standard press cycles in 25–40 seconds end-to-end. At 30 seconds per shot, that is 28,800 shots per day on a 24-hour cell, yielding 115,200 parts from a single four-cavity mold. This is why LSR dominates wherever volume exceeds 30,000 units/year — even though mold cost is higher, the throughput economics overwhelm the tooling premium.
Our 20+ machines running four-cavity tools gives us a theoretical combined output of over 2 million LSR parts per day across all sizes. In practice, we schedule 30,000 units/day across all processes as our committed daily capacity, accounting for changeovers, QC holds, and mixed-process scheduling.
HTV compression molding uses a hydraulic press with heated platens (160–200°C), a flat or matched-die mold, and a preformed charge of solid silicone compound. The press closes, pressure rises to 100–200 bar, and the compound flows under heat and pressure to fill the cavity, crosslinking as it goes. After 3–8 minutes (depending on part thickness and compound formulation), the press opens and the operator removes the part. Flash — the thin film of material that escapes between mold halves — is then torn or trimmed.
HTV is not an inferior technology. It has clear structural advantages in specific scenarios:
Large, thick parts. Parts with wall thickness above 6 mm or overall dimensions above 200 mm are typically more economical in HTV. LSR injection pressure and cure kinetics create residual stress in very thick sections; HTV's longer, lower-pressure cure is more forgiving.
Low volume runs. HTV molds for a medium-complexity part cost USD 600–2,500 versus USD 2,000–8,000 for LSR equivalent. At runs under 5,000 units total, HTV mold cost amortization wins decisively.
Complex color gradients and two-tone parts. HTV allows layering of differently colored compound sheets in a single mold to produce gradient effects. LSR two-shot processes exist but are far more complex and expensive to tool.
Material variety. HTV compounds come in a wider range of specialty formulations: high-temperature grades (up to 280°C continuous), conductive silicone, fire-retardant grades, very high shore (Shore A 70–80) rigid silicone gaskets. These specialty HTV compounds are well-established where equivalent LSR compounds either do not exist or are prohibitively expensive.
Flash is the defining limitation of HTV compression. Every HTV part has flash at the parting line. Flash removal is either manual (operators tear it by hand — fast but inconsistent), cryogenic (parts are tumbled in a liquid nitrogen environment where flash becomes brittle and breaks off — consistent, adds 0.5–1 day), or die-trimming (a secondary trim tool punches off flash — precise but requires additional tooling investment).
In 2023, our HTV line processed approximately 8 million units of kitchen silicone and promotional items. Every single one went through our trimming and inspection protocol. Flash acceptance AQL for Walmart-destined shipments is 0.0 on any flash taller than 0.3 mm. That zero-tolerance standard requires disciplined mold maintenance — we re-polish HTV mold parting surfaces every 30,000 shots.
Factor | LSR Injection Molding | HTV Compression Molding |
Raw material form | Two-part liquid | Solid gum compound |
Cure chemistry | Platinum (hydrosilylation) | Peroxide or platinum |
Mold temperature | 150–200°C | 160–200°C |
Cycle time | 15–45 seconds | 3–8 minutes |
Mold cost (simple part) | USD 2,000–8,000 | USD 600–2,500 |
Mold cost (complex) | USD 5,000–15,000 | USD 1,500–5,000 |
Flash generation | Near-zero (with precision shutoff) | Always some; requires trimming |
Shore A range | 10–80 | 20–80 |
Minimum wall thickness | 0.5 mm | 1.5 mm |
Automation potential | Very high (robotics, no-touch) | Moderate (operator handling) |
Color consistency | Very high | High (but preform dependent) |
Material cleanliness | Closed system — very high | Open mill process — moderate |
Best applications | Baby, medical, thin-wall, high volume | Kitchen, large parts, low volume |
Post-cure required | Not typically | Yes, for peroxide cure |
EU food contact | Achievable (LFGB §30/31) | Achievable (LFGB §30/31) |
FDA 21 CFR 177.2600 | Yes | Yes |
When a new project arrives at our facility, the process assignment is never arbitrary. Here is the exact decision tree our engineering team runs.
Decision Point 1 — Part weight and wall thickness.
Under 50 g and wall thickness under 4 mm: LSR preferred.
Over 150 g or wall thickness over 6 mm: HTV preferred.
Between those ranges: go to Decision Point 2.
Decision Point 2 — Flash tolerance.
Zero-flash or cosmetically critical parting lines: LSR required.
Flash acceptable if properly trimmed: HTV eligible.
Decision Point 3 — Annual volume.
Over 30,000 units/year: LSR economics typically win despite higher mold cost.
Under 5,000 units/year: HTV wins on total project cost.
5,000–30,000: run the math per project.
Decision Point 4 — Shore A hardness.
Shore A under 25 (very soft, gel-like): LSR only; HTV cannot reliably produce very soft parts without tack and handling issues.
Shore A 25–80: both processes viable.
Decision Point 5 — Application category.
Baby-contact / pacifier nipple / bottle nipple / medical: LSR strongly preferred for purity and traceability.
Promotional gifts / silicone wristbands / pet toys: HTV is typically cost-appropriate.
Kitchen utensils, oven mitts, baking mats: HTV with post-cure; LFGB-tested compound required.
Numbers from Q1 2026 on our combined LSR and HTV lines:
Average LSR cycle time across all active SKUs: 28 seconds (4-cavity)
Average HTV press time: 4.5 minutes (8-cavity)
Average HTV flash trimming time per part: 12 seconds (manual), 0 seconds (cryogenic)
LSR compound waste rate (cold runner system): 2.1% of input material
HTV compound waste rate (preform over-cut): 4.8% of input material
Inline AQL rejection rate, LSR: 0.8% (mostly parting line cosmetics)
Inline AQL rejection rate, HTV: 1.9% (mostly flash and color variation)
Post-cure oven time for peroxide HTV: 4 hours at 200°C
These numbers reflect genuine factory data. They are not marketing targets. If a vendor quotes you 0% rejection without inline AQL, ask how they know.
Both LSR and HTV parts often require secondary operations before they are finished goods. Secondary ops are where factory capability diverges sharply between commodity suppliers and a qualified manufacturer.
Overmolding. Bonding silicone over a hard substrate (ABS, PC, nylon). Requires surface priming (Chemlok or equivalent adhesion primer), precise bonding temperature, and mold design that seals around the hard component. We run overmolding on our LSR presses for products like silicone-grip infant spoons and tool handles.
Assembly. Multi-component silicone assemblies (e.g., bottle with silicone sleeve + silicone cap + silicone straw) require assembly jigs and functional testing. We assemble under controlled conditions with documented torque specs where applicable.
Printing. Silicone surfaces require activated ink systems or laser ablation before printing. Pad printing and silk screen printing on silicone are common; UV printing is possible but adhesion durability must be tested. We run print adhesion testing (cross-hatch tape test, rub test) on every decorated order.
Sterilization. For medical and baby products, post-production sterilization (gamma, EO, or autoclave) may be required. LSR parts are more consistently autoclavable without property changes than peroxide-cured HTV. Our LSR baby-contact parts are verified autoclave-stable to 121°C / 15 PSI / 30 minutes per standard cycle.
In 2021, a Fortune 500 baby brand was receiving pacifier shields from an HTV supplier. The shields met dimensional drawings but were generating consumer returns due to mold parting-line flash visible on the cheek-contact surface. The brand's regulatory team was also concerned about peroxide-cure by-product residuals in a product with prolonged infant skin contact.
We took on the project, transitioned the design to a 4-cavity platinum-cure LSR mold with a dedicated cold runner, and qualified the parts to FDA 21 CFR 177.2600 and EN 71-1 mechanical safety. Flash was effectively zero on the parting surface — below the 0.3 mm threshold that triggers tactile detection. Consumer return rates dropped measurably in the following season. The LSR mold cost was USD 4,200 versus the HTV mold at USD 1,400 — but that delta was recovered within 18,000 units of production at the volume differential.
We cannot name the brand under our NDA, but the project is representative of a transition we facilitate 8–12 times per year.
LSR can produce parts as soft as Shore A 10, which feels almost gel-like. HTV's minimum practical hardness is around Shore A 20–25; softer HTV compounds become difficult to handle and demold without tearing. If your design spec calls for Shore A under 25, LSR is the right process.
Both can achieve FDA 21 CFR 177.2600 compliance and LFGB §30/31 compliance — the certifications that define safe food and baby contact. LSR's advantage is process cleanliness: closed injection system, no operator handling of compound at an open mill, no preform cutting. For the highest-purity baby applications (pacifier nipples, bottle nipples), we default to platinum-cure LSR.
Yes. Our 4,500 m² facility has dedicated LSR injection cells (20+ machines) and dedicated HTV compression lines. The two production areas are physically separated to prevent compound contamination. QC documentation tracks which line, machine, and compound lot applies to each production order.
For a part of equivalent complexity, LSR molds cost approximately 2–3× more than HTV molds, driven by tighter shutoff tolerances, harder steel grades, and cold runner systems. A simple single-cavity HTV mold might cost USD 600–1,200; a comparable LSR mold runs USD 1,800–3,500.
Peroxide-cured HTV requires post-curing in a forced-air oven at 200°C for 4 hours to drive off residual peroxide by-products (primarily acetic acid in acetoxy-type systems). Platinum-cured HTV does not require mandatory post-curing, though a 2-hour post-cure at 180°C is standard practice to stabilize final properties. LSR parts do not require post-curing.
We offer virtual factory tours via video call and on-site visits for qualified buyers. Our YouTube channel at youtube.com/@mitoursiliconeproduct also features production process videos. Contact yfsalee@mymitour.com to schedule a tour.
Color variation in LSR comes from two sources: colorant lot variation (we use masterbatch from pre-approved suppliers and retain reference plaques from every lot) and metering ratio drift (our MMUs are calibrated weekly and alarmed for ratio deviation above 0.5%). We target Delta E under 1.0 between production runs for all standard colors and Delta E under 2.0 for metallics.
Yes. For medical-grade LSR projects, we provide Installation Qualification (IQ), Operational Qualification (OQ), and Performance Qualification (PQ) documentation packages. This is mandatory for Class I and some Class II medical device applications. Contact us with your device classification and regulatory pathway for a tailored validation plan.
The right process for your product — LSR or HTV — drives your mold cost, lead time, and certification path. Getting this decision wrong before tooling commit is an expensive mistake. We review process selection at zero cost as part of our standard DFM engagement.
Explore our manufacturing process detail
Review our materials capabilities
See our quality control protocols
Tour our facility overview
Email: yfsalee@mymitour.com
Phone: +86 199 2529 4106
Manufacturing process detail — anchor: "how an LSR project flows"
Materials capabilities — anchor: "compound selection and Shore A hardness"
Quality control protocols — anchor: "AQL inspection and process validation"
Factory overview — anchor: "4,500 m² Shenzhen facility"
Contact — anchor: "schedule a DFM review"
Peter Cui | 21 years of silicone manufacturing experience | 4,500 m² Shenzhen facility | Walmart-, Target-, and Disney-approved supplier | Contact: yfsalee@mymitour.com
