Why Some Exercise Balls Explode

& Others Do Not

Duane Priddy and Tom Peeler

Plastic Failure Labs

Imagine what would happen to this man if the ball he was placing his

weight on suddenly exploded!

I have worked as an expert on two matters Involving the explosion of a

fitness ball while athletes were lifting a 100 lb weight in each hand

during training. Both ended up with shattered bones in their arms and

months of excruciating pain and rehabilitation.

What Makes Balls Burst Resistant?

Flexible PVC foam

structure which interrupts

fracture propagation

Importance of Wall Thickness Uniformity

How Fitness Balls are ManufacturedManufactured by rotational molding. Plastisol (PVC + plasticizer + blowing agent)

is poured into a heated sphere where it coats the wall of the rotated sphere and

then is heated to the point that the chemical blowing agent generates CO2

Problems we have seen with balls:

1) Wall thickness variation

2) Debris embedded in the ball wall (during

manufacture)

3) Outside surface has most cells ruptured

during manufacture

4) Material flaw sensitivity

Burst Test Results of Four

Different Colored Balls

2 of 2 blue and 2 of 2 green exploded

2 of 2 gold and 2 of 2 brown did not

Why???

Flaw Sensitivity Testing

Only Material Difference

Noted was Trace Metals

Conclusions

• Exercise balls should be manufactured and tested to ensure

they are highly burst resistant and free from defects.

• Most exercise balls are manufactured in China and we have

found significant problems with material contamination and

wall thickness variation (e.g., >300% variation!)

• Key to burst resistance and safety is making the balls from a

material that is not sensitive to flaws.

• I believe that it is time for ASTM / ISO to develop stringent

manufacturing/testing standards for exercise balls.