The Air balloon () makes you immune to ground type moves and entry hazards such as Spikes and Toxic spikes(not immune against Stealth rocks) until it pops.
The balloon will pop as soon as you are hit with an attacking move. And even though Stealth rocks hit you they do not pop you since indirect damage does not pop the balloon.
>Gives the holder immunity to Ground-type moves, but pops when the holder is attacked. Indirect damage will not pop the balloon, and neither will Ground-type moves used against the holder. Breaking a holder's Substitute will also pop the balloon. The holder is also not affected by Spikes or Toxic Spikes.
It will also not have any effect if Gravity is in effect.
Hope I helped.