Silicone oils (PDMS) are among the most versatile industrial chemicals available. They lubricate, separate, defoam, insulate, and protect – at temperatures ranging from -60 °C to +250 °C. However, the wide range of cSt values, from 0.65 to 300,000, makes selection complex. This guide will help.
What is silicone oil?
Silicone oils are polydimethylsiloxanes (PDMS) – linear polymers of silicon and oxygen with methyl groups. Their unique properties result from the Si-O bond, which is more stable than the CC bond of organic oils.
- Thermal stability: -60 °C to +250 °C (briefly up to +300 °C)
- Chemical inertness: Resistant to oxidation, UV radiation, and ozone.
- Minimal viscosity change: Unlike mineral oils, the viscosity remains almost constant over a wide temperature range.
- Physiologically harmless: Non-toxic, skin-friendly
- Water-repellent: Hydrophobic surface treatment
- Electrically insulating: Dielectric strength >15 kV/mm
Viscosity ranges and applications
The viscosity (in centistokes, cSt, at 25 °C) determines the possible applications:
| viscosity | consistency | Typical applications | product |
|---|---|---|---|
| 0.65 cSt | Thin, like water | Cleaning, solvent replacement, heat transfer fluid | SILISIL Fluid 0.65 |
| 5–20 cSt | Like light oil | Spray demolding, textile softener, carrier | Bluesil 47 V 20 |
| 50–100 cSt | Like cooking oil | Lubricating coating, polishing, cosmetics | Bluesil 47 V 100 |
| 350–1,000 cSt | Like honey | Lubrication, damping, silicone paste base | SILISIL Oil 750 |
| 5,000–12,500 cSt | Thick liquid | Shock absorbers, anti-foam, potting compound | Bluesil 47 V 12500 |
| 60,000–100,000 cSt | Viscous | Joint sealant, silicone pastes, gaskets | Bluesil 47 V 60000 |
| 300,000 cSt | Almost paste-like | Vibration damping, special lubricants | SILISIL Oil 300,000 |
Application areas in detail
Lubrication and maintenance
Silicone oils lubricate plastic-on-plastic and rubber-on-metal contacts where mineral oils would attack the elastomers. Ideal for O-ring lubrication, valve seals, zippers , and guide rails of plastic components. Recommended viscosity: 100–1,000 cSt.
Demolding and release agents
Silicone oils offer excellent release properties on molds made of metal, plastic, and rubber. They can be used as an internal release agent (mixed into the molding compound) or an external release agent (applied to the mold surface). Viscosity recommendation: 50–350 cSt for spray application, 1,000+ cSt for brush-on release.
Electrical insulation
Silicone oils are used as a replacement for transformer oil (high dielectric strength, non-flammable), as a potting compound for high-voltage components , and as insulating fluid in cable glands. 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 process engineering. Concentrations as low as 1–50 ppm are sufficient.
Cosmetics and pharmaceuticals
Medium viscosity silicone oils (5–350 cSt) are used as lubricants in creams, conditioners in hair products , and as coatings for syringes and needles. For medical applications: Elkem Silbione range with the appropriate approvals.
Silicone oil vs. mineral oil vs. synthetic oils
| Characteristic | 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 |
| Lubricant properties of metal | Moderate | Good | Good |
| Price | Higher | Low | Medium |
Rule of thumb: Choose silicone oil when plastic/rubber contact, extreme temperatures, or food contact are involved. Mineral oil is for standard lubrication of metal surfaces. PAO is a good compromise.
Paintable silicone oils – The special problem
Standard silicone oils cause craters and wetting problems during subsequent painting. If you are using silicone oil in an environment where painting is also carried out, you need a special paintable silicone fluid. This contains modified siloxanes that do not permanently alter the surface tension.
→ SILISIL Silicone Fluid – Paintable Grade
Our product range
We stock silicone oils from Elkem Bluesil (47 V-series) and our own brand SILISIL in all common viscosities. Container sizes from 1 kg to 200 kg.
→ All 36 silicone oils and fluids
Further information
- Choosing the right Shore hardness: Explained from 0A to 90A
- Elkem silicones: the complete product range at a glance
- A day without silicone
- Biocompatible silicones: ISO 10993 and USP Class VI at a glance
- Silicone rubber: The complete guide to types, applications and market developments 2026
- Suitable products in the shop
- Request technical advice
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