Mine said 5-20 psi.  Different manufacturers have different specs.  Mine was pretty stiff with NO air in it though.  Kind of a bytch to get in as well.
Just installed it 2 days ago, trying it out tomorrow at Norwalk.  Can't wait to see how it does.
Here's a peek at my 1.49 60' launch in slo motion, WITHOUT the air bag (obviously)
http://media.putfile.com/Luckyslo-molaunch1