Material selection
Silicone (LSR) vs TPE
Both mold soft, rubber-like parts, and both overmold onto a rigid substrate. The decision between them is not softness, both cover a wide hardness range, it is temperature and biocompatibility. Silicone is a thermoset that survives −50 to 200 °C and carries medical documentation; TPE is a thermoplastic that molds on standard machinery for a fraction of the cost but cannot leave a narrower temperature band. The numbers below are the same published datasheet values used on each material's own page, set side by side.
| Silicone (LSR) | TPE (SEBS) | |
|---|---|---|
| Density | 1.10–1.20 g/cm³ | 0.90–1.05 g/cm³ |
| Hardness | 10–80 Shore A | 20–90 Shore A |
| Tensile strength | 6–11 MPa | 5–12 MPa |
| Elongation at break | 400–700 % | 500–800 % |
| Mold shrinkage | 2.0–3.5 % | 1.0–2.0 % |
| Service temperature | −50 to 200 °C | −40 to 70 °C |
| Relative cost | High | Low |
Published values for unfilled grades at 23 °C unless stated, taken from each material's own datasheet page. Confirm against the supplier datasheet for the grade you specify.
What Silicone (LSR) is
LSR is a two-part platinum-cured silicone injected cold into a hot tool, where it cures in seconds. Unlike a thermoplastic elastomer it is a true thermoset, so it does not soften with temperature and it holds its properties from −50 °C to 200 °C. It is the standard elastomer for medical and food applications because it is biologically inert, steam sterilizable, and available with full ISO 10993 and USP Class VI documentation. The trade-off is process and cost: it needs a dedicated LSR press running a hot tool against a cold, low-viscosity material, tighter shut-offs than a thermoplastic tool or it flashes, and a post-cure step, so both the tooling and the part carry a higher price than TPE.
What TPE is
SEBS-based TPE is the material behind almost every soft-touch grip on a consumer product. It runs on the same injection molding machines as any thermoplastic, drying is usually unnecessary, and specific grades bond chemically to ABS or PP during overmolding without a primer. It is weaker and less heat resistant than silicone, its service range tops out at 70 °C against silicone's 200 °C, and it carries no medical or food-contact documentation beyond standard food-contact and skin-contact certified grades, so it belongs on parts that are touched at room temperature rather than parts that see heat, sterilization, or patient contact.
Silicone against TPE
| Silicone (LSR) | TPE (SEBS) | |
|---|---|---|
| Service temperature | −50 to 200 °C, survives steam sterilization and hot environments | −40 to 70 °C, room-temperature and mild-heat use only |
| Biocompatibility and food contact | ISO 10993 and USP Class VI grades available, the default for patient-contact and food parts | Food and skin-contact certified grades exist, but no medical implant-grade documentation |
| Molding process | Thermoset, cold material into a hot tool (160–200 °C), needs a dedicated LSR press and post-cure | Thermoplastic, standard injection molding machine, melt 180–220 °C, mold 20–40 °C, no post-cure |
| Overmolding bond | Needs a primer or a self-bonding grade; substrate must tolerate the hot tool | Chemical bond to ABS or PP with a matched grade at room-temperature tool conditions |
| Tooling and part cost | High, dedicated LSR tooling and press time | Low, runs on standard equipment alongside the substrate shot |
| Compression set | Better long-term seal retention under sustained load | Soft grades take a set under sustained compression, not for structural seals |
Which one, for which part
- Medical seals, valves, or any patient-contact component is silicone's case: it is the material with ISO 10993 and USP Class VI documentation behind it.
- A part that has to survive steam sterilization or sits near a heat source needs silicone's 200 °C ceiling; TPE softens well before that.
- A soft-touch grip, button, or closure that only sees room temperature and a normal handling life is TPE's case: it costs less, molds on standard equipment, and bonds to PP as well as ABS.
- A seal under sustained compression, such as a gasket that has to hold its shape for years favours silicone's better compression set over a soft TPE grade.
- High volume consumer parts where tooling cost matters favour TPE; a dedicated LSR tool and press adds cost that only pays back where silicone's temperature or biocompatibility is actually needed.
Our status
Trumould molds both silicone LSR and TPE overmolding in-house, on the press range matched to each process, LSR on a dedicated LSR-capable machine, TPE on the standard thermoplastic range used for the rigid substrate. Send the part, the temperature and certification it has to survive, and target volume, and the quote states which elastomer is recommended and why, not just a price for whichever one you asked about first.
Specifying this part?
Send your CAD and target volumes. We come back with a price, a lead time, and any material or design notes that would reduce either.