Silicone oil 350 cSt and silicone oil 1000 cSt are two widely used medium-viscosity grades of linear polydimethylsiloxane (PDMS), also called dimethyl silicone fluid or dimethicone in relevant personal-care contexts. Both are typically clear, colorless, odorless and chemically non-reactive fluids with low surface tension, water repellency and good temperature stability.
Their chemistry is similar, but their processing behavior is not identical. The 1000 cSt grade flows more slowly and forms a more persistent, fuller-bodied film. The 350 cSt grade is easier to pump, spread and incorporate where lower drag is preferred.
The right choice therefore depends less on the question “Which viscosity is better?” and more on what the formulation must do during manufacture, application and use.
What Does cSt Mean?
The unit cSt, or centistokes, expresses kinematic viscosity. For silicone fluids, the stated grade is normally associated with a defined test temperature, commonly 25°C, but the purchaser should confirm the supplier’s specification and method.
Viscosity is temperature-dependent. A sample that feels thick in a cool warehouse will flow more readily after warming, even though it remains the same product. For meaningful incoming inspection, samples should be conditioned and tested under the agreed method and temperature.
Moving from 350 cSt to 1000 cSt does not change PDMS into a different chemical family. It primarily reflects a higher average chain length and greater resistance to flow. It also does not automatically make a product cosmetic grade, food grade or suitable for any regulated use. Grade status depends on the complete specification, manufacturing controls and supporting documentation.
Silicone Oil 350 cSt vs 1000 cSt at a Glance
| Selection factor | Silicone oil 350 cSt | Silicone oil 1000 cSt |
|---|---|---|
| Relative flow | Faster and easier to pour | Slower and more body-like |
| Pumping and dosing | Generally easier at ambient temperature | May require more attention to pump sizing and cool-temperature handling |
| Initial spreading | Quicker wet-out and easier rub-out | More controlled spreading with a richer feel |
| Film character | Lighter, thinner-feeling film | Fuller and generally more persistent film |
| Formulation use | Useful when processing ease and spreadability are priorities | Useful when substantivity, cushioning or longer-lasting surface effect is desired |
| Typical trial approach | Evaluate as the lighter starting point | Evaluate when 350 cSt is too mobile or insufficiently persistent |
These comparisons are practical tendencies, not universal performance guarantees. Substrate, dosage, surfactant system, solvent, fillers, application temperature and shear history can change the result.
Key Properties the Two Grades Share
Published product information from major silicone manufacturers shows why both grades appear across many sectors. WACKER describes its 1000 mm²/s linear PDMS as having minimal physical-property change over a broad temperature range, water repellency, low surface tension, chemical inertness, a low solidifying point and high heat resistance. Its current personal-care ingredient guide lists both 350 cSt and 1000 cSt dimethicone as clear, colorless liquids, with typical specific gravity around 0.97 and refractive index around 1.404.
These shared properties support use in areas such as:
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automotive and household care formulations;
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release and surface-conditioning systems;
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antifoam formulations;
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lubrication and maintenance products;
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rubber and plastic care;
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coatings and polishes; and
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personal-care formulations when the selected grade and documentation are appropriate.
The neat silicone fluid is not always the final formulation. Depending on the application, it may need to be emulsified, dispersed, blended with another viscosity or combined with functional additives.
When Silicone Oil 350 cSt Is Usually the Better Starting Point
Choose 350 cSt first when application ease and flow are more important than maximum film persistence.
Faster wetting and rub-out
The lower viscosity helps the fluid distribute across a surface with less mechanical effort. This can be useful in polish, protectant or maintenance formulations where the user expects easy application and minimal drag.
Easier transfer and dosing
At the same temperature and with comparable equipment, 350 cSt is normally easier to pour and pump than 1000 cSt. This can simplify small-batch dosing and reduce the time required for transfer from the original package.
Lighter sensory or surface feel
Where 1000 cSt feels too heavy, oily or slow to spread, 350 cSt may provide a better balance. The final effect still depends strongly on use level and the rest of the formulation.
A practical base for blending
350 cSt can serve as the lower-viscosity component in a blend designed to tune application, gloss and persistence. WACKER notes that linear silicone fluids across its viscosity range are mutually miscible, allowing formulators to adjust viscosity by blending compatible grades.
When Silicone Oil 1000 cSt May Perform Better
Choose 1000 cSt when body, cushioning or a more durable film is the higher priority.
More persistent surface effect
The higher viscosity can reduce mobility after application and help the silicone film remain on the substrate longer. This is often useful in polishes, conditioners and water-repellent surface treatments.
Richer application feel
In suitable personal-care or surface-care formulations, 1000 cSt can provide a softer, fuller or more velvety feel than a lower-viscosity grade. Dow lists spreadability, water repellency, heat stability and a soft skin feel among the features of its 1000 cSt PDMS fluid.
Better balance in durability-focused blends
Automotive appearance formulations often use more than one viscosity. Dow’s selection guide states that blends of intermediate- and higher-viscosity silicone fluids can balance gloss, durability, application ease and rub-out; the guide gives a 3:1:1 blend of 350, 1000 and 12,500 cSt as one example for optimizing shine and durability. That published ratio is a formulation starting point, not a universal recommendation, and should be validated on the intended substrate.
Application-by-Application Selection
Automotive and household care
For easy-spreading dressings and polishes, begin with 350 cSt. If the finish lacks depth, persistence or water resistance, evaluate 1000 cSt or a controlled blend. Check for streaking, dust pickup, rub-out time and gloss after aging—not only the appearance immediately after application.
Release and surface conditioning
350 cSt may give faster coverage and easier application. 1000 cSt may give a more durable residual film. The best option depends on the mold or substrate, application method, transfer risk and whether any silicone carryover could interfere with later coating or bonding.
Antifoam formulations
Both viscosities may be used as components in formulated antifoam systems, but neat PDMS viscosity is only one variable. Silica treatment, emulsifier package, droplet size, dispersion quality and the foaming medium can have a larger influence on performance. Always test the complete formulation in the customer’s actual process.
Personal care
Both 350 cSt and 1000 cSt appear in supplier guides for skin and hair formulations. The lower viscosity generally supports easier distribution; the higher viscosity can increase richness and substantivity. Confirm INCI naming, applicable regulations, impurity controls and grade documentation instead of selecting by viscosity alone.
Industrial lubrication and maintenance
350 cSt is easier to flow into narrow interfaces, while 1000 cSt may remain in place longer under low-load conditions. Neither grade should be selected solely from a generic application list. Load, speed, temperature, material compatibility and contamination risk must be reviewed.
Can 350 cSt and 1000 cSt Be Blended?
Compatible linear PDMS fluids can generally be blended to obtain an intermediate viscosity. However, the final viscosity should be measured rather than estimated by a simple arithmetic average. Viscosity blending is non-linear, and the result depends on the mass ratio and the actual viscosity distribution of each component.
A sensible laboratory workflow is:
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define the target processing and end-use behavior;
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prepare several small blends by weight;
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mix until fully uniform without entraining excessive air;
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condition samples at the agreed test temperature;
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measure viscosity using the specified method; and
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evaluate the blend in the complete formulation and on the real substrate.
What Buyers Should Confirm Before Ordering
A reliable purchase specification should cover more than “350 cSt” or “1000 cSt.” Ask for:
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the viscosity range, test temperature and method;
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appearance, density or specific gravity and volatile matter where relevant;
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grade designation and intended-use documentation;
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batch-specific COA, current TDS and SDS;
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sample availability for formulation trials;
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package size, net weight and lot traceability; and
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any application-specific limits required by the customer.
Do not assume that two products with the same nominal viscosity are interchangeable without testing. Molecular-weight distribution, volatile content and manufacturing controls may affect processing or finished-product performance even when both COAs show an acceptable viscosity.
Choosing the Right Grade
For a quick first decision:
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start with 350 cSt when you need easier pumping, faster spreading and a lighter film;
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start with 1000 cSt when you need more body, slower flow and a more persistent surface effect; or
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test a blend when neither grade alone provides the required balance.
ETOPDA supplies silicone oil 350 cSt and 1000 cSt for international customers. COA, TDS, SDS and samples are available for evaluation. To receive a relevant recommendation and quotation, provide the application, expected order quantity, destination, preferred packaging and any required grade or specification limits.
Frequently Asked Questions
Is 1000 cSt silicone oil higher quality than 350 cSt?
No. The number describes viscosity, not overall quality. A high-quality 350 cSt fluid can be more suitable than 1000 cSt when the formulation requires easier flow and spreading.
Are silicone oil and dimethicone the same?
Dimethicone is the INCI name used for polydimethylsiloxane in relevant personal-care applications. “Silicone oil” or “silicone fluid” is a broader industrial description. The required grade and documentation still need to be confirmed.
Which grade is better for polish formulations?
350 cSt usually offers easier application, while 1000 cSt can improve body and persistence. Many formulations use blends to balance rub-out, gloss and durability.
Can the two viscosities be mixed directly?
Compatible linear PDMS grades are generally miscible, but the blend should be prepared by weight, mixed thoroughly and tested. The final viscosity should not be calculated as a simple arithmetic average.
Does 350 cSt automatically mean food grade?
No. Dow offers a specifically designated food-grade 350 cSt product, illustrating that food-grade status comes from the defined product grade and supporting controls—not from the viscosity number itself.