SUITABLE FLOOR SURFACES
We recommend that the surface on which you exercise should be level and free of objects which may tear, puncture or damage the ball. You can use Swiss balls outdoors on grass or sand but ensure you thoroughly inspect the area for safety. You can use Yoga or Pilates mats, but their small size may not give adequate protection if the ball moves off the mat.
When exercising indoors, care must be taken to match the exercise with the slipperiness of the floor surface ie. polished timber floors, tiles, vinyl, carpet etc. This is because each surface type has a different co-efficient of friction (CoF) and if you push against a Swiss ball while exercising it may slip from under you and cause a serious injury.
NB: Exercising on padded mats such as judo/gymnastic mats is ideal for all ball exercises.
The “CoF” is also influenced by the ball surface (some are smoother than others) and by how firm it is inflated (how close it is to maximum diameter). The harder the ball, the less surface area touching the floor, and the more liable to slip. Similarly when you put all of your weight on the ball it will squash down giving greater surface contact area and it is less likely to slip when compared to exercises with just your legs on the ball.
This sounds technical, but it should not be ignored. Generally where the force vector (the direction of your push against the ball) of the exercise is greater than the CoF, the ball may slip.
NB: The more vigorous the exercise or the combined use of resistance aids (dumb bells or medicine balls) will increase the risk of slippage. Be careful!!