What is in a tennis can that puts pressure in the can?

Question

What makes the tennis can pop when you open a new can of tennis balls?

Answer 1

They put gas in the ball itself, but the can is only pressurized air.

A pressurized game ball including an air-permeable elastomeric wall defining a cavity containing a compressible inflation gas with the improvement being that the inflation gas includes predetermined mixed amounts of air and sulfur hexafluoride (SF6) gas which effectively enables the ball to retain its pressurized state within a desired range of pressures for a period of time significantly longer than the ball would remain pressurized if the inflation gas were air alone.

Answer 2

They compress the air to keep the balls fresh.

Answer 3

Compressed air seems like the simple answer, but it could be something else.

Answer 4

compressed air. Duh

Answer 5

Compressed Air!

Answer 6

The container is sealed and pressurized to keep the balls fresh to allow for the best bounce.