Silicone oils (PDMS) are among the most versatile industrial chemicals available. They lubricate, release, defoam, insulate, and protect—at temperatures ranging from –60 °C to +250 °C. However, the viscosity range of 0.65 to 300,000 cSt makes selecting the right product a complex task. This guide is here to help.
What is silicone oil?
Silicone oils are polydimethylsiloxanes (PDMS) —linear polymers composed of silicon and oxygen with methyl groups. Their unique properties stem from the Si-O bond, which is more stable than the C-C bond found in organic oils:
- Thermal stability: –60 °C to +250 °C (up to +300 °C for short periods)
- Chemical inertness: Resistant to oxidation, UV light, and ozone
- Minimal change in viscosity: Unlike mineral oils, the viscosity remains virtually constant over a wide temperature range
- Physiologically safe: Non-toxic, gentle on the skin
- Water-repellent: Hydrophobic surface treatment
- Electrically insulating: Dielectric strength >15 kV/mm
Viscosity ranges and applications
Viscosity (in centistokes, cSt, at 25 °C) determines the possible applications:
| viscosity | consistency | Typical applications | product |
|---|---|---|---|
| 0.65 cSt | As thin as water | Cleaning, solvent replacement, heat transfer fluid | SILISIL Fluid 0.65 |
| 5–20 cSt | Like light oil | Spray molding, fabric softener, carrier | Bluesil 47 V 20 |
| 50–100 cSt | Like cooking oil | Anti-seize coating, polishing, cosmetic finishing | Bluesil 47 V 100 |
| 350–1,000 cSt | Like honey | Lubrication, damping, silicone-based paste | SILISIL Oil 750 |
| 5,000–12,500 cSt | Thick | Shock absorbers, anti-foaming agents, potting compounds | Bluesil 47 V 12500 |
| 60,000–100,000 cSt | Viscous | Joint sealant, silicone compounds, gaskets | Bluesil 47 V 60000 |
| 300,000 cSt | Almost paste-like | Vibration damping, specialty lubricants | SILISIL Oil 300,000 |
Applications in Detail
Lubrication and Maintenance
Silicone oils lubricate plastic-to-plastic and rubber-to-metal contacts where mineral oils would damage the elastomers. Ideal for lubricating O-rings, valve seals, zippers, and guide rails on plastic components. Recommended viscosity: 100–1,000 cSt.
Demolding and Release Agents
Silicone oils provide excellent release properties on metal, plastic, and rubber molds. They can be used as an internal release agent (mixed into the mold compound) or as an external release agent (applied to the mold surface). Recommended viscosity: 50–350 cSt for spray application, 1,000+ cSt as a brush-on release agent.
Electrical insulation
Silicone oils as a substitute for transformer oil (high dielectric strength, non-flammable), as a potting compound for high-voltage components, and as an insulating fluid in cable bushings. Advantages over mineral oil: No aging process, no PCB formation, non-flammable.
Defoaming
Low-viscosity silicone oils (10–100 cSt) are highly effective defoamers in food production, paper manufacturing, wastewater treatment, and chemical engineering. Concentrations as low as 1–50 ppm are sufficient.
Cosmetics and Pharmaceuticals
Medium-viscosity silicone oils (5–350 cSt) used as lubricants in creams, conditioners in hair care products, and coatings for syringes and needles. For medical applications: the Elkem Silbione series with the appropriate approvals.
Silicone oil vs. mineral oil vs. synthetic oils
| property | silicone oil | mineral oil | PAO (synth.) |
|---|---|---|---|
| temperature range | –60 to +250 °C | –20 to +120 °C | –40 to +150 °C |
| Viscosity index | >300 | 80–120 | 120–170 |
| Rubber compatibility | Excellent | Bad | Moderate |
| Oxidation stability | Excellent | Moderate | Good |
| Lubricity of metal | Moderate | Good | Good |
| Price | Higher | Low | means |
Rule of thumb: Choose silicone oil when plastic or rubber contact, extreme temperatures, or food contact are involved. Use mineral oil for standard lubrication of metal surfaces. PAO is a good compromise.
Paintable silicone oils – The specific challenge
Standard silicone oils cause pitting and wetting issues during subsequent painting. If you use silicone oil in an environment where painting is also performed, you need a special paint-compatible silicone fluid. This contains modified siloxanes that do not permanently alter the surface tension.
→ SILISIL Silicone Fluid – Paintable Grade
Our product range
We carry silicone oils from Elkem Bluesil (47 V series) and our own brand, SILISIL, in all standard viscosities. Container sizes range from 1 kg to 200 kg.
→ All 36 silicone oils and fluids
