for the last few years, i’ve had a ironman balance ball as my desk chair with an isokinetics balance ball base. i like sitting on it while i work. it has been quite a while since i needed to add more air to my balance ball so when i tried the other day, my pump wasn’t working. the price for a new pump is around $6 +shipping while a new ball with a pump starts at $10 so i looked at getting another ball. unfortunately the one i had before is no longer around so i did some research on which one to get and found this article that gave some good pointers what to look for in a stability ball:
Be sure to use burst-proof stability balls, especially when using dumbbells or any other kind of weights while you are on the ball. If you were to stab a burst-proof ball with a knife, it would slowly deflate rather than pop. Also, burst-proof balls will be labeled with a weight limit to their effectiveness.
Stability balls are sold in sizes ranging from 45 to 75 cm. Your height will determine which ball is right for you. Remember, when sitting on a stability ball, your thighs should be parallel to the floor, at a 90-degree angle, and hips should be in line with or slightly higher than the knees,. If you are shorter than 5 feet 2 inches, use a 45-cm ball; if you are between 5 feet 2 inches and 5 feet 7 inches tall, use a 55-cm ball; if you are 5 feet 8 inches to 6 feet 2 inches tall, use a 65-cm ball; and if you are taller than 6 feet 2 inches tall, opt for a 75-cm ball.
The round surface of a stability ball offers enough instability to challenge your muscles; a ball that is low in air will reduce this benefit. If the ball flattens out when you sit or lie down on it, then it’s similar to a flat bench and less like a ball. Keep your stability ball fully inflated to reap the optimal fitness benefits.
A stability ball can range in price from $5 to $50, depending on brand, quality and durability. Pick a ball that best fits your budget and fitness goals. If you plan to use the stability ball for body weight exercise, use a basic ball. If you want to perform weight-training exercises on the stability ball, choose a durable ball.
Gaiam, SPRI, Resist-A-Ball and Fitball are some trusted brands that make stability balls of all sizes and colors. Notice if the ball is packaged with a pump; if not, use a bike pump or air compressor to pump up the stability ball.
read article by Dustin Bogle on Livestrong (Jun 14, 2011): What to Look for When Purchasing a Stability Ball