Process Oils in Tyre Building: The Hidden Ingredient Behind Modern Tyres

Every tyre contains more than rubber, steel and reinforcing materials. During manufacturing, several ingredients are combined to give the finished tyre the flexibility, strength and performance it needs on the road.

One of these important ingredients is process oil.

Most vehicle owners never come across the term, but process oils play an important role in many tyre compounds. They help make rubber easier to mix, process, and shape, while also influencing characteristics such as flexibility and compound performance.

The use of these oils has also changed considerably over the years. Distillate Aromatic Extract (DAE) oils were gradually replaced by lower-PAH alternatives such as TDAE, MES, and RAE.

So, what exactly do process oils do inside a tyre, and why are tyre manufacturers so dependent on them?

What Are Process Oils in Tyre Manufacturing?

Process oils, also known as rubber process oils (RPOs), are liquids added to rubber compounds during mixing.

They can be petroleum-based or, increasingly, derived from bio-based or recycled sources.

Raw rubber itself is difficult to process. It can be stiff, sticky, and resistant to the mixing and shaping processes used in a tyre factory. Process oil helps make the compound easier to work with.

It also helps other ingredients, including carbon black and silica, disperse more evenly throughout the rubber.

A simple way to understand this is to think about working with dough. If the dough is too stiff, it becomes difficult to roll and shape. A suitable amount of oil can make it easier to handle.

Rubber compounds work similarly. The right process oil helps the material move through mixers, mills, and extruders, eventually forming components such as treads, sidewalls, and inner liners.

Why Are Process Oils Important in Tyre Manufacturing?

A tyre compound is made from a mixture of materials rather than a single type of rubber.

Depending on the compound, these can include natural rubber, synthetic rubber, carbonblack, silica, sulphur, and various chemical additives.

When these ingredients are mixed on an industrial scale, friction and heat are generated. Process oil helps the compound remain workable during this stage.

Its main functions include:

Improving flow: It helps rubber move through mixers and extrusion equipment.
Reducing mixing energy: A workable compound can be processed more efficiently.
Controlling hardness and flexibility: The type and amount of oil influence the characteristics of the finished rubber compound.
Helping filler dispersion: Process oil can assist in the proper distribution of the materials such as carbon black and silica throughout the compound.
Extending the rubber compound: Oil can allow manufacturers to achieve the required compound volume while controlling material costs.

Without suitable processing aids, many rubber compounds would be considerably more difficult to mix, shape and manufacture.

This is why process oil has remained an important part of tyre manufacturing for decades.

How Did Process Oils Become Part of Tyre Manufacturing?

The use of oil-extended rubber developed during the expansion of synthetic rubber production in the mid-20th century.

As synthetic rubber became increasingly important after the Second World War, rubber manufacturers found that adding petroleum-derived aromatic extracts could facilitate processing of synthetic rubber, particularly styrene-butadiene rubber (SBR).

The practice, known as oil-extended rubber, eventually became common throughout the tyre industry.

For many years, Distillate Aromatic Extract (DAE) was one of the most widely used process oils.

DAE had good compatibility with rubber and provided useful properties such as flexibility and grip. However, it contained relatively high levels of polycyclic aromatic hydrocarbons (PAHs).

Some PAHs are associated with serious health risks, including cancer risk following prolonged exposure.

As scientific understanding of these compounds developed, regulatory requirements became stricter, particularly in Europe.

Why Did the Industry Move Away From DAE?

European restrictions on high-PAH extender oils forced tyre manufacturers and suppliers to explore alternatives that could provide similar processing and performance characteristics while meeting the new requirements.

EU restrictions on high-PAH extender oils took effect in 2010, significantly limiting the use of traditional high-PAH oils such as DAE in tyre and rubber applications covered by the relevant requirements.

The change had a major effect on the tyre and rubber industries.

Manufacturers had to reformulate compounds, while oil suppliers developed alternatives with much lower levels of the regulated PAHs.

This transition eventually established several newer process oils as important materials in modern tyre production.

From DAE to TDAE: A Major Change in Tyre Manufacturing

One of the most important replacements for DAE was Treated Distillate Aromatic Extract (TDAE).

TDAE retains many of the processing characteristics that tyre manufacturers value while meeting the relevant PAH requirements.

It provides good compatibility with rubber and is widely used in tyre compounds where manufacturers need a balance between processing behaviour and finished-tyre performance.

Other process oil families also became important, particularly:

MES — Mild Extract Solvate
RAE — Residual Aromatic Extract
Naphthenic oils

As each has different characteristics, tyre engineers select the oil according to the requirements of the particular compound.

DAE and Modern Process Oils Compared

Feature	DAE	TDAE	MES	RAE
PAH level	High	Low	Low	Controlled
Regulatory position	Not permitted where applicable PAH limits are exceeded	Compliant	Compliant	Compliant where applicable
Rubber compatibility	Very good	Very good	Good	Good
Cold-temperature flexibility	Good	Very good	Good	Moderate
Typical modern use	Phased out	Tyre compounds, including passenger tyres	General rubber compounds	Selected tyre and rubber compounds

The important point is that the industry did not simply stop using process oils. Instead, it moved toward grades that offered the required rubber performance while meeting tighter health and environmental requirements.

Types of Process Oils Used in Modern Tyre Building

Different tyre compounds require different properties. As a result, no single process oil is ideal for every application.

Aromatic-Based Oils: TDAE, MES and RAE

These oils are important in tyre compounds because of their compatibility with rubber and their contribution to compound processing and performance.

TDAE, in particular, is widely used in modern tyre formulations.

Naphthenic Oils

Naphthenic oils are valued for their low-temperature characteristics and colour stability.

They can be used in applications where flexibility at lower temperatures is important, as well as in certain lighter-coloured rubber products.

Bio-Based and Renewable Process Oils

The tyre industry is also exploring process oils made from renewable and recycled feedstocks.

Plant-derived oils and other alternative raw materials are being considered as manufacturers consider new avenues to reduce dependence on conventional petroleum resources and support wider sustainability targets.

However, petroleum-based process oils continue to account for a substantial share of overall use.

Which Process Oil Is Used for Which Application?

Oil Type	Typical Application	Main Advantage
TDAE	Passenger and performance tyre compounds	Good balance of processing and rubber performance
MES	General rubber compounds	Versatility and regulatory compliance
RAE	Selected tyre and rubber compounds	Performance and durability requirements
Naphthenic	Selected rubber and tyre compounds where low-temperature flexibility and other formulation characteristics are required	low-temperature flexibility
Bio-based oils	Selected sustainable or eco-focused compounds	Renewable or recycled feedstock potential

Actual formulations vary from one tyre manufacturer and compound to another. The oil is selected as part of the overall formulation rather than in isolation.

Where Does Process Oil Enter the Tyre Manufacturing Process?

Process oil is introduced during the rubber mixing stage.

A simplified tyre manufacturing sequence looks like this:

1. Mixing

Raw rubber is combined with materials such as carbon black, silica, chemicals, and process oil in an industrial mixer.

The oil helps the compound process and assists with the distribution of the ingredients.

2. Milling and Extrusion

The mixed compound is processed into different tyre components.

These can include the tread, sidewall, and other rubber layers.

The processing characteristics affect how easily it moves through the machinery and forms the required tyre components.

3. Tyre Building

The individual components are assembled around the tyre carcass.

Steel belts, textile reinforcement, and other components are incorporated according to the tyre design.

4. Curing

The assembled tyre is placed into a mould and subjected to heat and pressure.

During curing, vulcanisation takes place. This creates the cross-linked rubber structure that gives the tyre its required strength and elasticity.

Process oil therefore enters the manufacturing process well before the tyre reaches the curing stage.

Its influence is mainly through the rubber compound and its processing characteristics.

What Is Changing in 2026?

Process oils remain an area of attention for both tyre manufacturers and chemical suppliers.

European chemical regulations continue to place limits on high-PAH process oils, which keeps traditional DAE-type materials out of applications where they do not meet the required limits.

At the same time, tyre manufacturers are paying increasing attention to the wider chemical profile of tyre formulations.

Although 6PPD is not a process oil, its environmental discussion illustrates the broader chemical and sustainability challenges facing the tyre industry.

This is part of a broader shift in the tyre industry toward understanding not only how a chemical performs during manufacturing, but also what happens to it throughout the tyre's service life and after the tyre reaches the end of its useful life.

Another developing area is the use of bio-based and recycled feedstocks.

As tyre companies set sustainability and carbon-reduction targets, process oils made partly from renewable or recycled sources are receiving greater attention.

How Do Tyre Manufacturers Choose a Process Oil?

Selecting a process oil is not simply a matter of choosing the cheapest available material.

Tyre engineers generally have to consider several factors:

Regulatory compliance: The oil must meet applicable PAH and chemical requirements.
Compound requirements: Different rubber compounds require different processing and performance characteristics.
Climate: Tyres designed for colder conditions may require different compound characteristics from tyres designed for hot climates.
Cost and availability: A material must be commercially practical and consistently available.
Sustainability targets: Manufacturers increasingly consider renewable and recycled feedstocks when developing new formulations.

The final choice is therefore part of a much larger tyre-compounding process.

Why Process Oil Matters to the Tyre You Drive On

The amount of process oil used in a tyre may be small compared with the total weight of the tyre, but its role in rubber processing is significant.

It helps manufacturers turn a difficult-to-process rubber mixture into a compound that can be mixed, extruded, assembled and eventually cured into a finished tyre.

The choice of oil can also influence important compound characteristics.

That is why process oil is much more than simply an ingredient added to make rubber softer. It is one of the materials that helps tyre engineers control how a rubber compound behaves during manufacturing and in the finished tyre.

Conclusion

Process oil is one of the less visible materials involved in tyre manufacturing, but it plays an important role in making rubber compounds workable and consistent.

The industry has changed significantly from the period when high-PAH DAE oils were widely used. Today, tyre manufacturers can choose from materials such as TDAE, MES, RAE and naphthenic oils, along with newer bio-based and recycled alternatives.

The change has been driven by a combination of regulation, material science, manufacturing requirements and growing interest in sustainability.

For drivers, process oil is not something they normally need to think about when buying a tyre. For tyre manufacturers, however, choosing the right oil is an important part of developing a rubber compound that can be manufactured reliably and deliver the required performance on the road.

Frequently Asked Questions

1. What is process oil used for in tyres?

Process oil helps soften and improve the workability of rubber compounds. It also helps with the mixing and dispersion of ingredients such as carbon black and silica.

2. Why was DAE replaced?

Traditional DAE contained relatively high levels of PAHs. Regulatory restrictions on high-PAH extender oils led the tyre industry to move toward alternatives such as TDAE, MES, and other compliant grades.

3. Is TDAE used in modern tyres?

Yes. TDAE is widely used in modern rubber and tyre compounds because it provides useful processing and performance characteristics while meeting applicable PAH requirements.

4. Can tyres be manufactured without process oil?

Some specialised rubber formulations may use little or no conventional process oil, but process oils remain widely used because they make many rubber compounds easier to process and manufacture.

5. Are bio-based process oils replacing petroleum-based oils?

Bio-based and recycled process oils are gaining attention, particularly as tyre manufacturers pursue sustainability targets. However, conventional petroleum-based process oils still account for a large share of current usage.

Disclaimer

This post is intended for general informational purposes only. It is not technical, engineering, regulatory, or investment advice. Process-oil regulations and requirements can differ between countries and may change over time. Manufacturers, buyers and other industry professionals should consult current regulations and qualified technical or regulatory specialists before making commercial or compliance decisions.