Silicone Oil 350 cSt

Understanding 350 cSt Silicone Oil

350 cSt silicone oil is a medium-viscosity PDMS grade that occupies the transition zone between the freely-flowing general-purpose grades (50–100 cSt) and the distinctly thick high-viscosity grades (1,000+ cSt). At room temperature, 350 cSt flows slowly from a container — comparable to light motor oil or thin honey — and forms a noticeably persistent film on surfaces.

For a practical reference: if you tilt a container of 350 cSt silicone oil 45 degrees, the liquid begins moving after a brief hesitation. On a glass surface, a drop of 350 cSt will spread to cover approximately 5 cm² over 10 seconds, compared to 10+ cm² for 100 cSt. This slower spreading and more robust film formation distinguish 350 cSt from lower grades.

Viscosity-temperature behavior: approximately 180 cSt at 100 °C and 700 cSt at 0 °C. Flash point exceeds 300 °C. The molecular weight corresponds to approximately 14,000–18,000 Da.

Recommended Applications for 350 cSt

Textile finishing: 350 cSt PDMS is used directly in textile finishing baths when a heavier silicone coating is desired — for example, in outerwear fabrics requiring silicone-enhanced water repellency and stiffness retention, or in industrial protective garments needing enhanced surface lubricity. The higher viscosity provides greater film thickness per unit of active silicone versus lower grades.

Electronics potting and gap filling: 350 cSt PDMS flows into small gaps and clearances in electronic assemblies, displacing air and moisture from around components. While not a structural adhesive, it provides dielectric protection and thermal conduction enhancement at the component level. It is commonly used to fill vibration-prone connectors and seal around wire-to-board terminations.

Process lubricant for plastic extrusion: During thermoplastic extrusion (PVC pipes, polyethylene film, polypropylene profiles), 350 cSt PDMS is sometimes introduced as a process aid — applied to the barrel or die — to reduce melt fracture and die buildup. Its thermal stability at extrusion temperatures and compatibility with most thermoplastics make it suitable.

Dielectric cooling fluid: 350 cSt is one of the standard viscosities for transformer dielectric fluid. Its viscosity provides good heat convection within transformer tanks while remaining thin enough for efficient circulation in forced-flow cooling systems.

Laboratory and industrial heating baths at higher temperatures: For heating baths operating above 150 °C, 350 cSt PDMS has lower evaporative loss than 100 cSt over long operating periods. The higher molecular weight means lower vapor pressure at elevated temperatures.

How to Select the Right Viscosity

Choose 350 cSt when:

• You need more film persistence than 100 cSt provides
• Temperature range is −50 °C to +250 °C with moderate viscosity stability required
• Textile finishing requires heavier silicone deposition per pass
• Electronics potting or sealing requires flowing into medium-sized gaps

Move down to 100 cSt when: faster spreading or lighter feel is needed, or when 350 cSt is too thick for atomization in spray systems.

Comparison with Adjacent Viscosities

350 cSt vs. 100 cSt: 100 cSt spreads much more readily and feels lighter, making it the preferred grade in cosmetics and standard heat transfer applications. 350 cSt provides a heavier, more durable surface coating and is preferred when persistence and film thickness matter more than spreadability.

350 cSt vs. 1,000 cSt: 1,000 cSt is clearly thick — it pours slowly and is the lower end of what is considered "high viscosity." 350 cSt is still relatively fluid in comparison. For defoaming applications, 1,000 cSt is more effective; for textile finishing requiring a softer, more uniform coating, 350 cSt is preferred.

Ordering and Packaging

350 cSt is a well-stocked grade available from major silicone distributors. Standard packaging: 200 L steel drums and 1,000 L IBC totes. Bulk tanker delivery available for large volumes. The higher molecular weight means 350 cSt is slightly denser than 100 cSt (0.970 g/cm³) and requires slightly higher temperatures or pressure for drum pumping in cold weather.

Shelf life: 2+ years in sealed containers. COA should confirm: viscosity (350 ± 15 cSt), specific gravity (0.970 ± 0.003), flash point (>300 °C). For food-contact applications, request food-grade certification confirming compliance with FDA 21 CFR 172.878 or 178.3570.