Almost every custom silicone quotation starts with one fork in the road: compression molding with solid HTV rubber, or liquid silicone rubber (LSR) injection molding. Choosing the wrong one does not usually produce a bad part — it produces a part that costs too much, or tooling you outgrow in a year.
Quick answer
Use compression molding for low to medium volumes, thicker sections, large flat parts and high-hardness compounds. Use LSR injection molding for high volumes, thin walls, micro features, tight tolerances, and clean-process medical or infant products.
Side-by-side comparison
| Compression molding (HTV) | LSR injection molding | |
|---|---|---|
| Raw material | Solid high-consistency rubber, pre-weighed preforms | Two-part liquid silicone, metered and mixed |
| Tooling cost | Low to moderate | 2–4× higher |
| Cycle time | 2–6 minutes | 20–90 seconds |
| Typical tolerance | ISO 3302-1 M2–M3 | ISO 3302-1 M1–M2 |
| Flash | More; manual or cryogenic trimming | Minimal with cold-runner tooling |
| Labour content | Higher | Lower, largely automated |
| Best volumes | 500 – 50,000 / year | 50,000+ / year |
1. How each process actually runs
Compression molding. A pre-weighed slug of uncured rubber is placed in an open heated cavity. The press closes, pressure and heat (typically 170–200 °C) cure the part in minutes, then it is demolded and deflashed. It is forgiving, cheap to tool and ideal for gaskets, keypads, kitchenware and thick-section parts.
LSR injection molding. Two liquid components are metered, mixed and injected into a closed, heated mold through a cold runner. Cure happens in seconds to a couple of minutes. The process is closed, repeatable and easily automated — which is why it dominates medical devices, baby teethers and precision seals.
2. Let geometry make the first cut
- Thin walls under 1 mm or long flow paths: LSR fills where solid rubber will not.
- Micro textures, sharp radii, small holes: LSR reproduces detail more faithfully.
- Thick solid sections (over ~10 mm): compression cures more evenly and avoids sink.
- Large flat parts and mats: compression tooling is far cheaper for the projected area.
- Overmolding onto plastic or metal inserts: both work, but LSR with self-bonding grades gives the most consistent adhesion.
3. Then run the total-cost math
Compare 12 months of real demand, not a per-piece price:
Total cost = tooling + (unit price × annual volume) + expected scrap + secondary trimming labour.
A typical example: compression tooling at USD 1,200 with a unit price of USD 0.42 versus LSR tooling at USD 4,500 with a unit price of USD 0.19. At 10,000 pieces per year compression wins clearly; at 40,000 pieces LSR is already cheaper, and the gap widens every year the tool keeps running.
4. Quality differences buyers actually notice
- Flash lines. Hand-trimmed compression parts show a witness line; on consumer-facing surfaces specify tear-trim tooling or cryogenic deflashing.
- Repeatability. LSR shot volume is machine-controlled, so part weight varies far less across a run.
- Cleanliness. The closed LSR process reduces contamination risk, which is why it is the norm for infant and medical products.
- Color changeover. Compression handles small color runs more economically; LSR pigment purging costs machine time.
5. A practical decision path
- Is the part medical, infant-contact or tolerance-critical? → LSR injection.
- Is annual volume above ~50,000? → LSR injection.
- Are walls thicker than 8–10 mm or the part large and flat? → compression.
- Is this a market test or first production run under 10,000? → compression, then re-tool once demand is proven.
Related reading: choosing Shore A hardness and how to choose a silicone manufacturer.
Looking for a compression molding manufacturer in China? See our silicone compression molding manufacturer page.
Decided that liquid silicone is the right process? See our LSR injection molding manufacturer in China page.
Need custom silicone rubber keypads or elastomer keypad mats as finished OEM parts? See our silicone keypads manufacturer page.
Planning the tooling budget? Read custom silicone mold cost and MOQ.
Sourcing keypads? Read our buyer’s guide to custom silicone keypads.
Working with Tongsheng
Dongguan Tongsheng Electronic Technology Co., Ltd. has manufactured silicone rubber molds and silicone products since 2014. We run in-house CNC tooling, compression and liquid silicone injection molding, and a testing lab, from a 2,000+ sqm ISO 9001:2015 certified factory in Humen Town, Dongguan, with 100+ staff and 15 engineers. Food-grade (FDA / LFGB), medical-grade and industrial-grade compounds, Shore A 10–80, Pantone and RAL color matching.
Send 2D/3D drawings (STP, IGS, PDF) and we quote within 24 hours — request a quote, email coraycn@gmail.com, or message us on WhatsApp.