Silicone for Custom Molded Components — Properties, Applications & Specifications
Table of Contents
Silicone (VMQ) maintains crosslinked polymer chain flexibility across a temperature range of –60°C to +230°C because its Si–O backbone has a bond angle and rotation energy fundamentally lower than carbon-based elastomers, preventing the glass transition stiffening that makes organic rubbers brittle in cold and oxidatively degrade in sustained heat. That thermal stability prevents seal extrusion failures, compression set-induced leakage, and surface cracking that nitrile and EPDM experience when cycling between cryogenic storage temperatures and high-heat operating conditions. Fenlora molds silicone in 20–80 Shore A hardness across diaphragm seals, custom gaskets, and grommets for medical device, food processing, and aerospace applications where thermal cycling and regulatory compliance are non-negotiable requirements.
Material Properties & Specifications
| Common names / abbreviations | Silicone Rubber (VMQ) |
|---|---|
| Polymer structure / monomer system | Polydimethylsiloxane |
| Tg (°C) / Brittle Point | -86 °C to -127 °C |
| Density (g/cm³) | 1.10 - 1.60 |
| Hardness range (Shore A/D) | 20 - 90 Shore A |
| Tensile strength (MPa) | 10.3 |
| Elongation at break (%) | 100 - 800 |
| Rebound / tanδ (temp + freq) | 30 - 60 % Rebound |
| Compression set (%) | 7 - 10 % |
| Continuous service temp (°C) | -62°C to 215°C |
| Environmental & Fluid Resistance | Ozone: Outstanding |
| ASTM D2000 Callouts | M7GE705 A19 B37 EA14 E016 E036 F19 |
| Electrical properties | Vol Res: 1x10^14 - 1x10^16 ohm-cm |
| Thermal properties | Thermal Cond: 0.13 - 0.35 W/mK |
| Tear Resistance | Tier 1 - Basic |
| Abrasion Resistance | Tier 1 - Basic |
| Gas Impermeability Resistance | Tier 1 - Basic |
| Oxygen Resistance | Tier 5 - Excellent |
| Ozone Resistance | Tier 5 - Excellent |
| Weathering Resistance | Tier 5 - Excellent |
| Oil Resistance | Tier 2 - Limited |
| Acid Resistance | Tier 2 - Limited |
| Alkaline Resistance | Tier 1 - Basic |
| Water Resistance | Tier 4 - Strong |
| Flame Resistance | Tier 5 - Excellent |
When to Specify Silicone
Silicone (VMQ) is the correct material choice when thermal range, physiological inertness, or long-term outdoor weathering define the service requirements — and the wrong one when fuel, steam, or dynamic abrasion loads are present.
| Use Silicone when… | Avoid Silicone when… |
|---|---|
| Operating temperatures cycle below –40°C or exceed +175°C continuously | Exposure to hydrocarbon fuels, oils, or lubricants (swell and strength loss) |
| FDA 21 CFR or USP Class VI biocompatibility is required for fluid contact | High-pressure steam environments above 120°C (hydrolysis degrades VMQ) |
| Long-term UV, ozone, or outdoor weathering resistance is required | Dynamic abrasion or high-wear sliding contact surfaces |
| Electrical insulation with stable dielectric properties across temperature is needed | Low-cost, high-volume commodity applications where NBR or EPDM would perform adequately |
| Permanent compression set resistance is required across –60°C to +200°C thermal cycling | Applications requiring tensile strength above 1,500 psi without reinforcement |
Silicone’s compression set resistance at elevated temperatures is driven by its Si–O–Si backbone stability: unlike NBR or neoprene, which undergo thermal oxidative crosslink scission and permanently deform under sustained load at temperatures above 120°C, silicone retains elastic recovery because the Si–O bond energy (450 kJ/mol) resists oxidative chain breaking. In practice, this means a silicone O-ring or gasket that has been compressed in a high-temperature static seal will return to its original geometry when removed — a property that determines whether a seal retains sufficient contact stress to prevent leak paths after thermal cycling.
Custom Parts We Make in Silicone
Fenlora manufactures silicone components across compression, transfer, and injection molding processes to meet dimensional tolerances and compliance requirements for demanding thermal and hygienic environments.
→ Diaphragm seals — Silicone’s flex fatigue resistance and compression set recovery make it the standard choice for pump and valve diaphragms in pharmaceutical processing, where repeated flexural cycling at elevated CIP/SIP cleaning temperatures would cause nitrile to crack and permanently deform.
→ Custom gaskets — Flat and profile gaskets in food-grade silicone meet FDA 21 CFR 177.2600 for continuous fluid contact; the material’s surface chemistry resists microbial adhesion and withstands repeated autoclave sterilization without hardening. [Explore our custom gasket].
→ Grommets and cable pass-throughs — Silicone’s stable dielectric constant across –60°C to +200°C makes it appropriate for wire and cable protection in aerospace and EV battery enclosures where thermal cycling would embrittle PVC or standard EPDM grommets. (See Fenlora rubber grommets)
→ O-rings and face seals — Silicone O-rings are specified in HVAC, semiconductor equipment, and cryogenic fluid systems where operating temperatures fall outside the service window of standard NBR or EPDM compounds.
If your drawing specifies silicone (VMQ) or you’re working from functional requirements around temperature range, biocompatibility, or weathering, contact our engineering team to discuss compound selection and hardness range: Contact us
Industries That Use Silicone
Medical & Life Sciences
Silicone diaphragm seals, custom gaskets, and tubing connectors are standard components in fluid handling, diagnostic equipment, and implant-adjacent devices. The driving requirement is USP Class VI or ISO 10993 biocompatibility combined with autoclave sterilization tolerance; silicone’s inert Si–O chemistry and resistance to repeated 134°C steam cycles without hardening or leaching make it uniquely suited where organic elastomers would release plasticizers or degrade.
Gaskets, pump diaphragms, and valve seals in silicone are used throughout CIP (clean-in-place) processing lines, filling equipment, and conveyance systems. Silicone meets FDA 21 CFR 177.2600 and resists the repeated thermal cycling and alkaline/acidic cleaning agents that cause NBR or SBR to crack and contaminate product streams.
Automotive & Electric Vehicles
Silicone gaskets and seals are used in engine bay thermal management, battery pack sealing, and high-voltage connector grommets. As EV battery enclosures introduce sustained high-temperature environments and require UL 94 flame-rated seals, silicone compounds with flame-retardant additives are increasingly specified over standard EPDM for thermal runaway protection interfaces. (Link to automotive industry)
Compare Materials
Silicone is the correct default for thermal range and biocompatibility — but if your application loads the part in a way that exploits silicone’s mechanical weaknesses, a different compound will outlast it.
| If your application involves… | Consider instead |
|---|---|
| Oil, fuel, or hydraulic fluid exposure | Nitrile (NBR) |
| Extreme chemical or solvent resistance | Viton (FKM) |
| High dynamic flex and tear resistance | Natural Rubber (NR) |
| High abrasion and mechanical wear | Polyurethane (AU/EU) |
| Moderate oil + weather resistance | Neoprene (CR) |
| Air/gas impermeability | Butyl (IIR) |
| Cost-sensitive general-purpose use | SBR |
Not sure which material fits your application? Send us your requirements and we’ll recommend the right compound.