bladder bags

I found these drink bags on ebay a while ago and have been testing them with the idea of using them as bladders. so to convert one into a bladder i have drilled a hole in the lid and glued in a hose fitting but you could use some brass tube. just out of curiosity, i connected it to a little geared water pump and started filling. I wanted to know when and where it would burst but surprisingly the pump stalled out and the bag is solid with no leaks. even squeezing it as hard as I could with both hands i couldn't burst it.

https://www.ebay.co.uk/itm/364223176229

you can also get much bigger version with a hose fitting already connected.

https://www.ebay.co.uk/itm/155510765063

I have been using the kids “floaty” that you blow up and they go around the kids upper arm. Picked them up at my local Dollar General for about 3 dollars I think. Get 4 bags. It has been working well

Back in the day we made our own bag’s, we used rubber latex and a stocking/tights, pull the stocking over a bottle of the size you wish to make your bag, then paint on the rubber latex, keep doing this until you have four or five layers, leave to dry, plug the open end with some form of stopper.
The bag will always go back to the same shape were a swim bladder will most of the time not.
Fred