In middle school we built a drum with pig‘s bladder.

Take a cardboard tube (like for posters), pull a bladder over it and fix it with a string wound around it.

Changed its tuning quite a bit with air moisture and smelled a bit funny (but not gross). I kept it around as a toy for quite a while.

Interesting! How long would you estimate that bladder lasting in that state? Days, weeks, or years?

Mine lasted years. But I cannot remember if our teacher may have prepared the bladder first.

Some instructions on the web recommend to put it in saltwater for 24 hours, so that may be how we received them.

I suspect you could probably source pork bladder in quantity, relatively cheap from slaughterhouses. Never know that kind of thing might be a specialty delicacy somewhere and it turn out you can't afford it. It might turn out they're the vital ingredient for automobile airbags this whole time and we never knew.