We recently analyzed the coefficient of friction of 91 contact materials currently listed on our friction coefficient table.

And the findings?

We noticed that 30 contact materials have a known coefficient value ≥ 0.5 and 61 contact materials have a coefficient value less than 0.5

From the analysis, here is a list of the top 11 contact materials with the highest known coefficient of friction.

NOTE: It’s wrong to say ask questions like “what materials have the highest coefficient of friction?”

REASONS: Coefficient of friction (C.O.F) is a surface property and not an intrinsic property of individual materials.

This means that coefficient of friction can only exist between two materials in contact.

Let’s simplify this further.

Given 3 materials;

Material A, Material B, and Material C

You can’t talk about the coefficient of friction of Material A as “stand-alone” material.

But rather, the coefficient of friction of Material A on Material B or Material A on Material C.

More like a pair combination and it’s logical since friction itself is a contact force; meaning it must involve two contact surfaces.

Having this in mind, the right question will be:

what contact materials have the highest coefficient of friction? (or paraphrased in any form that signifies material pairs).

And the right answer is clearly outlined in the table above.

Contact Materials with the Highest C.O.F: HOW THE ANALYSIS WAS CARRIED OUT

Few days ago, we published a complete guide on coefficient of friction which contains a friction coefficient table that outlines the C.O.F of over 91 known contact materials.

We needed only materials with high coefficient of friction so we screened the list and selected only materials with coefficient of friction greater than 0.5.

About 30 contact materials fell into this limit.

A graph indicating the coefficient of friction on the y-axis and the contact materials on the x-axis was plotted.

Here’s the result:

The graph clearly shows the peak points with the 11 highest coefficient of friction.

Some coefficient values exist in ranges (i.e. x-y).

For the purpose of the plot, the average value was calculated and used on the graph.

For example:

The coefficient of friction of solid on rubber is 1.0 – 4.0

The average coefficient is 2.5. This is a preferred value for graphical purposes only.

The chart below further outlines the 11 contact materials with the highest C.O.F in descending order.

Further Observations:

Using the average values, we discovered that 8 of these contact materials have a friction coefficient ≥ 1.0

Contact Materials with friction coefficients equals or greater than 1.0

This accounts for roughly 73% of our list with only 27% falling below coefficient value of 1.0

Contact materials with such high friction coefficient value are required in automobile industries and engineering components to:

1. Quickly bring a body to rest
2. Avoid motion of specific parts. 

QUESTION: What contact materials have the highest coefficient of friction?

ANSWER: Solid on Rubber (1.0 – 4.0)

There are only two factors that affect the coefficient of friction and they are:

1. The nature of the surfaces in contact.
2. The friction type (Static, kinetic, or rolling friction)

The coefficient of friction is a surface property. Therefore, its value is constant for a given combination of material surfaces.

The coefficient of friction for given pair of surfaces only varies across different surface conditions like wet, dry, and greasy surfaces.

Nevertheless, these variations are known for different surface pairs through experimental analysis and specified on a friction coefficient table.

How does the nature of contact surfaces affect the coefficient of friction?

Primarily, friction is caused by the interlocking of tiny surface irregularities known as asperity.

The extent of asperity interlocking varies according to the nature of surfaces in contact.

This means that different surface pairs will either possess a higher or lower friction resistance based on their individual surface property.

As a result of this, the coefficient of friction will be dependent on the nature of contact surface under consideration.

It’s worth knowing that all objects have microscopic rough planes regardless of how smooth or polished they may appear.

NOTE: Coefficient of friction does not exist for a single material but rather for a given pair of surfaces in contact.

Therefore, it’s wrong to say things like: “What’s the coefficient of friction of a rubber chair”

Friction is a contact force, it must involve 2 interacting surfaces, same principle applies to friction coefficients.

Having this in mind, a better question phrase to the format described above will be:

What’s the coefficient of friction of a rubber chair on a concrete floor?

What’s the coefficient of friction of a rubber chair on a rubber tile?

Sounds better now right? (you can just nod in agreement✨).

The answer is provided in the table below.

This table is extracted from Afrilcate’s guide on Static friction coefficient, you can see the complete table here:

Comprehensive List of Static friction Coefficient

Variations of Contact Surfaces with Coefficient of Friction

As mentioned earlier, the coefficient of friction varies across different pairs of surfaces.

Also for a given surface pair, the coefficient changes according to the surface condition.

Surface condition means either wet, dry or greasy surfaces.

How does the type of friction affect the coefficient of friction?

Generally, there are three types of friction:

1. Static friction: The friction force between two surfaces at rest relative to each other.
2. Kinetic friction: The friction between two surfaces that moves or slides relative to each other.
3. Rolling friction: The friction force that resists the rolling motion of an object against a surface. Also known as rolling resistance or rolling drag.

These three friction types possess friction coefficients known as the coefficient of static friction, the coefficient of kinetic friction, and the coefficient of rolling friction respectively where:

Coefficient of static friction: is the numerical value that quantifies the degree of stickiness between a static object and its contact surface.

Coefficient of kinetic friction: is the numerical value that quantifies the friction intensity of a sliding surface relative to another.

Coefficient of rolling friction: is a numerical value that quantifies the degree of motion resistance between a surface and a rolling object.

The static friction coefficient has a higher value when compared to other friction types for a given set of contacting surfaces.

This is because the prolonged/undisturbed state of static position allows more time for asperity locking and molecular bond formation unlike objects in the sliding or rolling state.

That’s why it’s much easier to keep a moving object in motion than to initiate the motion of the object from rest.

Again, the coefficient of rolling friction has the least value when compared to other friction coefficient types for a given set of contacting surfaces.

Variation of friction types with Coefficient of friction

Enjoyed the read?

See other similar friction articles by Afrilcate:

1. What is the direction of static friction?

2. 6 major causes of static friction

3. 7 major Factors that increase static friction

4. 11 Contact Materials with the Highest Coefficient of Friction