Non-Filled. There are commercial stress balls that are not filled, rather they are made out of a special pliable foam rubber called closed-cell polyurethane foam rubber. The manufacturer injects a special liquid into a mold, resulting in a chemical reaction that creates carbon dioxide bubbles.
These are made by injecting the liquid components of the foam into a mold. The resulting chemical reaction creates carbon dioxide bubbles as a byproduct, which in turn creates the foam. Stress balls, especially those used in physical therapy, can also contain gel of different densities inside a rubber or cloth skin.
They may look like simple foam toys, but a lot more goes into making stress balls than you might think. See the process from beginning to end!
Gel stress balls provide a therapeutic option for releasing stress or pent-up emotions. The inside of the ball is filled with a silicone-based gel, sometimes infused with. Gel balls have more of a liquid, squishy feel when squeezed and are less .
Funky Egg Colorful Splat 'N' Stick Ball Squishy Toys 6 Pack Stress Relief Yolk. .. so when they leak or break, the liquid inside doesn't stink and it's not toxic.