So i've been using an exercise ball as a chair for a while now and i've found them somewhat annoying to deal with (fetish and all that aside) as they tend to roll around all the time and need way too much effort and concentration to keep them stable and balanced in order to sit somewhat comfortably. And as a result of that i dont use them that often unless im "in the mood" so to speak. Then i found these "peanut" shaped exercise balls in my local super duper mart and decided to give these a go as their shape seemed a lot more easy to deal with ( as there is mostly only two axis of movement you have to deal with instead of all 3) and would be a perfect candidate for heatstretching for something more "rideable" due to their shape.
Back in november when i got the first peanut ball, i managed to heat stretch under just a hot shower. to almost double the original size of 45x45x90cm to 70x70x140! Although this is just an approximation as i didn't have a tape measure on hand at the time to measure with.
Sadly this particular ball only lasted a day or so as it had burst during the night when i was asleep

it was absolutely huge!
Unfortunately it was the last one on stock too in the mart so i couldn't get another one to be a bit more modest with so untill a week or so when they got some back in stock. So just the other week i bought another one and this time decided to only stretch it to about 50x50x100cm which has so far lasted pretty well. Although i do have to inflate it to a quite firm state with little give to get to that size.
For me the size is quite optimal as it can be ridden and used as a "bench" chair or a "saddle" chair and is much more comfy to use as traditional exercise balls although they dont have quite as much bounce to them (with bigger basesizes i dont think this would be an issue though). Its pretty fun to ride with it and doubles as a pretty good chair too as it has the positives and comfyness of a traditional ball without the major drawbacks of a ball!
If you dont like exercise balls i would still give peanut balls a definite go! Especially with a little heat stretching, these can be a very versatile.
(this might come off as a bit rambly or incoherent as i am not a native english speaker but i hope you got the jist

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