Airplane vs. Sea Level Air Pressure

The air pressure at sea level is much greater than at altitude.  An airplane is pressurized, but I think it's roughly to an equivalent altitude of 8000ft.  So, the air pressure is significantly less than at sea level.  To show this concept, I opened my water bottle during the flight so that the pressure in the bottle equaled that of the cabin pressure (~8000ft equivalent).  With the bottle back at sea level, the greater ambient pressure crushes the bottle.