Short answer: choose LSR (Liquid Silicone Rubber) for precision small parts, transparent parts and high volumes; choose HCR (High Consistency Rubber) for thick-walled large parts, sustained high-temperature use, or early-stage sampling. Neither is inherently better — they fit different geometries and volumes.
LSR and HCR are the two mainstream silicone molding routes. Chemically both are organosilicones; the differences lie in feedstock form, molding method and mold design — and those three differences cascade into precision, cost, lead time and heat resistance. The table below lays them out side by side.
| Dimension | LSR | HCR | What it means for you |
|---|---|---|---|
| Feedstock form | Two-part liquid, A/B metered and mixed | High-viscosity solid, requires milling and weighing | HCR is more labour- and cleanliness-dependent |
| Molding method | Liquid injection molding, fully automated | Compression or transfer molding, manual loading | LSR delivers better batch consistency for long runs |
| Hardness range | Roughly 10–60 Shore A, down to ~5 A | Roughly 30–80 Shore A | For very soft parts (below 20 A), prefer LSR |
| Dimensional precision | High; ±0.05 mm achievable | Moderate; typically ±0.10 mm and up | Precision small parts and sealing lips favour LSR |
| Mold cost | Higher; cold-runner system usually required | Lower and structurally simpler | For small trial runs, HCR lowers upfront risk |
| Unit cost | Lower at high volume | More economical at low volume | The crossover is usually in the thousands of pieces — calculate per project |
| Production efficiency | Short cycle, continuous automated output | Longer cycle with manual handling | Tight lead time plus high volume favours LSR |
| Temperature range | Typically −50 °C to +200 °C | Typically −60 °C to +230 °C | For sustained use above 200 °C, HCR is safer |
| Appearance & clarity | High transparency, optical grade possible | Usually translucent or natural, limited clarity | Light-guiding and transparent parts favour LSR |
| Best-fit geometry | Small, thin-walled, precise, complex | Medium-to-large, thick-walled, irregular, with inserts | Thick parts in LSR risk shrinkage and voids |
| Typical applications | Keypads, sealing lips, baby teats, medical tubing, optical parts | Large O-rings, gaskets, industrial rollers, heat-resistant parts | — |
| Project stage | Mass production, precision-critical, visible parts | Sampling, simple geometry, cost-sensitive | A common path: validate in HCR, mass-produce in LSR |
Four Typical Scenarios
Small precision seals — which one?
Choose LSR. For miniature seals, tolerance and lip consistency are everything. LSR injection holds ±0.05 mm more reliably, and cold runners drastically reduce flash, eliminating much of the de-flashing labour. For parts under 5 mm, or sealing lips down to 0.3 mm, LSR is effectively the only practical option.
High volume, lower unit cost — which one?
Usually LSR. The mold costs more upfront, but automation strips out most manual labour, so the unit cost advantage grows with volume. That said, the crossover point varies: for simple, not-too-small parts, HCR’s lower tooling cost can still win at moderate volumes. Ask your supplier for quotes at your actual annual volume before deciding.
Sustained operation above 200 °C — which one?
Choose HCR. HCR’s typical continuous-service ceiling is around 230 °C versus roughly 200 °C for LSR, and under sustained rather than brief peak heat that gap determines service life. Above 230 °C neither general-purpose silicone is suitable — move to a high-temperature specialty compound or re-evaluate the material route.
Just validating a design — without heavy tooling spend?
Start with HCR compression molding. The molds are simpler and cheaper, which suits rapid iteration while the design is still moving. Once drawings and feel are locked, evaluate the switch to LSR for production. Note that LSR and HCR molds are not interchangeable — switching processes means new tooling, and that cost should be budgeted upfront.
Selection Checklist
- Fix the hardness first: below 20 Shore A, LSR is effectively the only route
- Characterise the geometry: minimum wall thickness, maximum size, metal inserts or not
- Count annual volume: below a few thousand pieces HCR often wins; tens of thousands favour LSR
- Specify the temperature ceiling and duration — distinguish peak from continuous
- Confirm whether high transparency, light guiding or optical-grade appearance is required
- Confirm whether overmolding, two-shot or multi-material construction is needed
- List the testing items required by your target market (food contact, medical, flame retardancy)
- Evaluate sampling and production processes separately so conversion tooling does not blow the budget
FAQ
Can LSR and HCR be mixed or run on the same line?
No. The feedstock form, metering system and mold design (cold runner vs conventional compression mold) are entirely different, requiring separate equipment and tooling. Mixing one into the other causes cure anomalies, cosmetic defects and off-spec performance. Choosing a process means choosing a production line — which is why switching processes requires new molds.
Is LSR always more expensive than HCR?
Split it into two accounts. Tooling: LSR costs more, due to cold runners and tighter machining. Unit cost: LSR is usually cheaper, thanks to automation, short cycles and less de-flashing. So low-volume projects tend to total less in HCR, high-volume in LSR. The practical test is simple — ask for total-cost quotes in both processes at your real volume.
Can both processes meet food-grade or medical-grade requirements?
Both can, and the deciding factor is the compound grade and its test reports, not the molding process itself. Each process has food-contact and medical grades available, and each can meet the required cleanliness and traceability. Ask suppliers to name the specific compound and provide third-party reports matched to your target market, rather than accepting a blanket "food-grade" claim.
LXYSILICONE runs both LSR injection and HCR compression lines, so we can advise on the right route at the sampling stage — including which one totals less at your specific volume.