In synthetic rubber production, small changes can have a big impact. A compound that mixes smoothly can save time. A compound that runs the same way every day can reduce scrap. That’s one reason many rubber producers use process oils, and naphthenic oils may be the go-to type for certain applications. Questions? Contact us.

Naphthenic process oils may be a great fit for some synthetic rubber applications, especially when you need a helpful mix of solvency and low-temperature flow. 

In other cases, paraffinic process oils may be the better choice, depending on the polymer, fillers, and performance goals. (Automotive interiors, for example.)

This guide focuses on what naphthenic process oils do, what to look for when you buy, and offers a few product options to consider.

Suzanne Kingsbury, Director of Quality

The Role of Process Oils in Synthetic Rubber Production

Process oils (also called plasticizers) are added to rubber compounds to help with processing and performance. They can:

• Reduce compound viscosity (how “thick” it feels during mixing)
• Improve flow during forming steps like extrusion and molding
• Support filler dispersion (help ingredients spread more evenly)
• Increase tack (stickiness) in some compounds
• Improve softness by plasticizing the rubber
• Help manage cost when used as an extender (when the formulation allows it)

In real-world terms, the goal is usually the same: make the compound softer, easier to process, and easier to control.

When Naphthenic Oils May Be a Smart Fit: 4 Criteria to Consider

Rubber process oils are often grouped into three families: paraffinic, naphthenic, and aromatic. Each family has a different mix of hydrocarbon structures. That changes how the oil behaves in rubber.

Naphthenic oils are often chosen when you need:

• Good solvency (compatibility) with many materials

• Low wax content, which often supports lower pour points and better cold flow

• A “middle ground” option when you want strong processing support without leaning heavily into highly aromatic oils

That said, paraffinic oils can be a great fit in many rubber systems, too. The best choice depends on the application, not the oil “category.”

1. Solvency and the Aniline Point

Solvency is a simple idea: it’s the oil’s ability to blend well with the rubber and other ingredients. Better compatibility can help a compound come together more smoothly during mixing.

One common solvency indicator is the aniline point. Aniline point is measured using a standard test method (American Society for Testing and Materials standard D611, a.k.a. ASTM D611). It is used to help characterize hydrocarbon mixtures. 

In general:

• Aromatic hydrocarbons have lower aniline point values
• Naphthenic oils have intermediate aniline points and solvency
• Paraffinic hydrocarbons tend to have higher aniline point values

You do not need to treat the aniline point as the only decision factor. However, it’s a useful “signal” when comparing options and considering compatibility.

2. Pour Point and Cold Flow

Pour point is the temperature at which an oil stops flowing. If your plant ships or stores materials in winter conditions, cold flow can matter a lot.

Naphthenic oils are often known for low wax content, which can support lower pour points and better low-temperature flow in many cases.

If cold handling is a real issue for your operation, pour point is one of the first specs to check.

3. Color Stability

Color stability matters most when making light-colored parts or when your customer has strict appearance standards.

If appearance is part of your quality targets, look for process oils designed and documented for more consistent color.

4. Compliance and Market Pressure: A Quick Note On PAHs

Some rubber markets also pay close attention to polycyclic aromatic hydrocarbons (PAHs). 

In the European Union (EU), REACH (Registration, Evaluation, Authorisation of Chemicals) restrictions limit PAHs in tires sold in Europe, which pushed many buyers toward low-PAH naphthenic oil alternatives.

Not every application is a tire application, and not every buyer has EU requirements. But it’s still helpful to keep compliance needs in mind early, before you lock in a spec.

A Simple Checklist for Choosing a Naphthenic Process Oil

Before you choose a grade, start with your application and your constraints:

• Solvency Needs: Do you need stronger compatibility to support mixing and dispersion? (Aniline point can help guide this.)

• Viscosity Needs: Do you need a heavier oil for processing control, or a lighter oil for easier flow and handling?

• Low-Temperature Needs: Will the oil need to pour and pump in cold conditions? (Check pour point.)

• Color Targets: Do you need a color-stable option for light compounds?

• Documentation Needs: What properties must be documented for your customer or your internal quality system?

And remember: naphthenic oils may be the right fit in some compounds, while paraffinic oils may be the better fit in others. The “best” choice is the one that matches the application.

Naphthenic Oil Options from Renkert Oil

Once you know what you are optimizing for, you can narrow your choices quickly. 

Below are examples of three naphthenic options Renkert Oil supports for rubber and compounding needs. (Values below are pulled from current product documentation on file and are shown here as buyer-friendly highlights. Full technical datasheets are available by request.)

Renoil 1100: When Solvency Is A Priority

If your main goal is stronger solvency behavior and a heavier viscosity profile, Renoil 1100 may be a good starting point.

Benefits include:

• Solvency signal: Aniline point is reported at 171°F (77°C)

• Heavier viscosity profile: Helpful when you need more body and control in processing

• Clear documentation: Useful when you need consistent reporting for quality files

This is often the kind of option you consider when compatibility and processing feel are driving the decision.

Renoil 500-X: When You Want A More Color-Stable Naphthenic Option

If you want naphthenic performance but also care about appearance targets, Renoil 500-X may be a better match.

Benefits include:

• Color stability angle: ASTM color is reported at 0.5

• Cold handling support: Pour point is reported at -6°F (-21°C)

• Compliance note: Documentation states it meets 21 CFR 178.3620(c) mineral oil requirements (as written on the COA (certificate of analysis))

This is a strong option to consider when color and cleanliness matter more than they do in many black compounds.

Renoil 50-S: When Very Low Pour Point Matters Most

If cold flow is your top constraint, Renoil 50-S is built around that need.

Benefits include:

• Very low pour point: Listed at -83°F (-64°C) (typical)

• Light viscosity: Supports easy handling and flow

• Solvency signal: Aniline point is listed at 150°F (66°C) (typical)

This is the option many buyers look at when cold-weather pumping, drum handling, or low-temperature performance is on the line.

Quick Naphthenic Oil Guide: Which One Should You Start With?

If you want a simple way to narrow choices:

• If you want heavier viscosity and a strong solvency signal, start with Renoil 1100.

• If you want a more color-stable naphthenic option, start with Renoil 500-X.

• If your biggest need is very low pour point, start with Renoil 50-S.

And if naphthenic does not look like the best fit for your compound, consider paraffinic process oils. The right answer depends on the application.

Renkert Oil: the Right Process Oil for Your Application & Reliable Support

Buying a process oil is not about choosing a “best” one-size-fits-all product. It’s about selecting the best match for your polymer system, fillers, processing conditions, and performance goals.

That’s where Renkert Oil can help. Tell us what you’re making, what your line struggles with, and what specs matter most. 

We’ll guide you through comparing options, choosing a naphthenic grade that fits, or confirming when a paraffinic process oil makes more sense, so you can keep your compounds consistent and your production moving.

We’re here to help! Contact Renkert Oil today.

 

FAQs: Naphthenic Process Oils

1) What is a process oil in synthetic rubber?
A process oil is added during compounding to help rubber mix, flow, and process more smoothly. It will also help you fine-tune compound softness and performance.

2) Are naphthenic process oils always better than paraffinic oils?
No. Naphthenic process oils may be the best fit for some compounds, but paraffinic process oils may be the better choice for others. The right option depends on your polymer, fillers, process, and end-use needs.

3) What does “solvency” mean for a rubber compound?
Solvency is a simple way to talk about compatibility—how well the oil blends with rubber and other ingredients. Good solvency can help a compound come together more evenly and consistently. Solvency is especially important for polar additives and polymers.

4) What is the aniline point, and why does it matter?

Aniline point is a standard test value used to categorize oil type and solvency behavior. In general, lower aniline point values mean higher solvency, while higher values are found in more paraffinic oils.

5) How does pour point affect production or logistics?
Pour point is the temperature where an oil stops flowing. A lower pour point can make cold-weather storage, pumping, and handling easier.

6) When does color stability matter in process oils?
Color stability matters most for light-colored parts or products with strict appearance specs. If you mainly make black compounds, color will be less critical, though some buyers still prefer tight color control.

7) How do I know if I need a light oil or a heavier oil?
Light oils can be easier to handle and may support flow, while heavier oils can support more processing control in some formulations. Higher temperature applications favor heavier oils with their lower volatility. Your equipment, filler package, and targets usually point you toward the right range.

8) Can I swap from one process oil to another without changing anything else?
Sometimes, but not usually. Even similar oils can change processing feel or final properties, so it’s smart to test a small trial batch before switching at scale.

9) Which Renkert Oil naphthenic oil product should I start with?
If your top goal is solvency, start with Renoil 1100. If you want a more color-stable naphthenic option, look at Renoil 500-X. If cold handling is the priority, start with Renoil 50-S. Give us a call and we will review our full range of options.

10) What should I ask my supplier before I choose a naphthenic oil?
Ask about typical property ranges, lead times, packaging, documentation support, and how they handle supply continuity—so your production plan isn’t affected by avoidable delays.

11) Do these oils work for all synthetic rubbers?
They can fit many systems, but not every oil is a match for every polymer. The best results come from matching the oil to the polymer type, filler load, and performance needs.

12) How can Renkert Oil help with process oil selection?
Renkert Oil can help you compare naphthenic and paraffinic options, narrow in on a best-fit grade, and build a supply and logistics plan that keeps your specialty oils arriving on time and on spec.