Silicone Oil Guide: Viscosities, Applications, and Selection (0.65 to 1'000'000 cSt)

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, their viscosity range of 0.65 to 1,000,000 cSt 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 C-C 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:

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 to 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 as an external release agent (applied to the mold surface). Viscosity recommendation: 50 to 350 cSt for spray application, and from 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 to 100 cSt) are highly effective defoamers in food production, paper manufacturing, wastewater treatment, and chemical process engineering. Concentrations as low as 1 to 50 ppm are sufficient.

Cosmetics and pharmaceuticals

Medium viscosity silicone oils (5 to 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

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 Oil Paintable Grade (paintable silicone fluid)

Our range

We carry silicone oils from Elkem Bluesil (47 V-series) and our own brand SILISIL in viscosities from 0.65 to 1,000,000 cSt. Container sizes from 1 kg to 200 kg.

→ All silicone oils and fluids in the shop