Coefficient of Friction (COF) is a measurement of the amount of force one object must overcome to move over another. Knowing the Coefficient of Friction of polyurethane is critical to selecting the appropriate durometer (hardness level) of the polyurethane.

1. POLYURETHANE PRODUCTS
“From Prototype to Production”
Understanding Polyurethane
Coefficient of Friction
www.Sunray-Inc.com

2. What is Coefficient of Friction?
• Coefficient of Friction (COF) is a measurement of the
amount of force one object must overcome to move over
another.
– Example: When a polyurethane wheel rolls over a surface,
such as a concrete floor, the wheel must overcome a
frictional force to move.

3. Why is Coefficient of Friction Important?
• Knowing the Coefficient of Friction of polyurethane is
critical to selecting the appropriate durometer (hardness
level) of the polyurethane.
• The harder a polyurethane (the greater the durometer),
the lower the Coefficient of Friction tends to be.

4. Why is Coefficient of Friction Important?
• Polyurethanes with a higher durometer are typically able
to withstand a greater load capacity and have a higher
slip resistance.
• For detailed information on the maximum load capacities
of polyurethane drives wheels, see this chart:
www.sunray-inc.com/load-capacities/

5. Why is Coefficient of Friction Important?
• Engineers can use the known Coefficient of Friction
between polyurethanes and various surfaces to calculate
the amount of applied force (drive force) needed to
propel a polyurethane wheel over a surface.
• Polyurethanes with a low COF and a high durometer will
require very little applied force to maintain movement.

6. POLYURETHANE COEFFICIENT OF FRICTION
Surface = Polished Steel
DUROMETER
(HARDNESS)
Friction Coefficient
WET
DRY
70A
0.26
0.71
75A
0.25
0.66
85A
0.28
0.77
90A
0.26
0.70
95A
0.29
0.68
55D
0.27
0.60
Table 1
Polyurethane Coefficient of Friction on Polished Steel

7. How is Coefficient of Friction Measured?

8. How is Coefficient of Friction Measured?

9. How is Coefficient of Friction Measured?
• There are two main types of Coefficient of Friction that
may be measured:
1. Static Friction
2. Kinetic Friction.

10. Static vs. Kinetic
Coefficient of Friction
• Static friction occurs when the frictional force applied to
an object is greater than the applied force (driving force),
resulting in the object remaining motionless.
• Kinetic friction occurs when the applied force (driving
force) on an object is greater than the frictional force
pushing against the object, resulting in movement.

11. 2
Static Coefficient of Friction: Polyurethane Durometers on Dry Surfaces
1.8
Coefficient of Friction
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
Standard Steel
Aluminum
Wood
Concrete
Formica
60A
0.9
2
0.97
0.97
1.11
85A
0.35
0.76
0.63
0.7
0.35
92A
0.1
0.28
0.42
0.49
0.28
75D
0.1
0.17
0.17
0.21
0.28
Table 2
Static Coefficient of Friction of Polyurethanes

12. Factors Impacting Coefficient of
Friction for Drive Wheels
• There are several factors that may impact the Coefficient
of Friction of a polyurethane drive wheel, including:
–
–
–
–
–
the type of surface the polyurethane wheel is in contact with,
the amount of contact pressure at varying speeds,
whether the diameter and durometer is rated for the load weight,
the condition of the surface (wet, dry, clean, dirty, rough, smooth),
whether additives were utilized to alter the polyurethane.

13. Selecting a Polyurethane Compound
• For assistance selecting the appropriate polyurethane
compound for your needs, or help identifying the optimal
durometer/hardness level for your polyurethane
wheels, visit:
www.sunray-inc.com
Sunray, Inc. offers expert service and design help.
All polyurethane products are 100% made in the USA!