Update: I bought two of them and good thing. They are great and my wife has claimed one!

Sitting Discs
Looks like a good idea.

Easy to transport.

And it self inflates

And can be a mini ball when fully inflated.

Only $35.95 CAD. Get yours now.

The most advanced and versatile sitting disc you have ever used!
The ProActive Disc will strengthen abdominal and back muscles plus
improve posture, balance and core stability - all while you sit!
It’s so comfortable and easy to use!

• Great for air travel, or use in a car or bus, at school or work!
• Lightweight and portable - easily rolls to fit into any briefcase
  or pack.
• Self-inflating Therm-a-Rest® technology with easy adjust
  valve.
• Durable construction and superior craftsmanship allows the ProActive
  Disc to be used for balance exercises and stretches.
• Portable seat for hiking or camping . Take it with you anywhere!
• Helps insulate you from both hot and cold seating surfaces.
• Highest quality fabric is both comfortable and washable.