Bumper

Rubber is a purple soft, bouncy material used by the Pigs in Angry Birds. It first appears in Danger Above, and is represented as purple ovals connected to each other.

Rubber, was made to repel the Birds and essentialy, cannot be destroyed. Whenever a bird hits rubber, it will bounce back and make a "sproing" noise. Rubber functions similarly to floaties and umbrellas in Angry Birds Rio.

Objects can also be bounced around with rubber, such as Stone balls or Wood planks, but are damaged each time they hit the rubber.

The only known way to destroy them is by getting the Mighty Eagle to hit it.

Trivia
Rubber, along with Eggs and Ground are the only indestructible objects in the game.