If something is rubberier, it means it is more like rubber, stretchy, and bouncy.
Rubberier things are often fun and playful.
Examples:
The rubberier ball bounces higher.
Her rubberier shoes are more comfortable.
The rubberier band stretches farther.
I wish my bed was rubberier so I could bounce on it.
The rubberier the trampoline, the higher you can jump.
The rubberier the toy, the more fun it is to play with.