Print in TPU and fill with lead shots and sand. The sand will help muffle the sound but not required. Lead shot is needed to give it weight.

I filled it about 1/3 up with lead but you can add as much as you like to fit your style.

They are very satisfying to juggle and don't roll much when they hit the ground.

You will need to pause your printer half way through printing to fill. I used support from bed only.

Balls are a remix from https://www.thingiverse.com/thing:6025