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.
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.