Here’s the water bottle I took with me on my flight from Oregon to Arizona:
I took several swigs during the flight.
When we landed and I retrieved it from the pocket, I noticed it was caved in. So I took the above picture of it.
Can you explain it?
(It returned to normal shape when I opened it.)
I’m not wise enough to explain it, but I have experienced the same phenomenon.
I wonder what those flights are doing to our bodies?
‘Tis a simple change in air pressure. Though it’s well known that airliner cabins are pressurized, the pressure changes while in flight. The air preasure at takeoff is relative to the air pressure of the airport the plane takes off from. PDX, I would assume, is less (to be safe here, I’ll overestimate) than 300 feet above sea level. So, that’s you’re starting atmospheric pressure. As the plane climbs the cabin air pressure is gradually adjusted up, reaching a maximum equivalent to the atmospheric pressure of 8,000 feet. Thus, when you opened your bottle in mid-flight, it equalized with the pressure of approximately 8,000 feet. When you arrived in Arizona, you were most likely several thousand feet below 8,000 feet above sea level, thus the pressure was greater on the outside than the inside of the bottle when it was last opened, causing the sides to cave in. Opening the bottle once more, equalized the pressure yet again causing it to return to its “resting” state.
I’m not totally sure of all the technical details of the cabin pressure requirements on planes, but I think it has something to do with it being easier on equipment to maintain a virtual 8,000 ft. pressure, than sea level, AND I believe it may be a safety issue as well—If a plane was kept at sea level pressure the whole flight, the difference in air pressure at 35,000 feet may well compromise the integrity of the aircraft, the worst case scenario causing the aircraft to “explode” because of the difference in air pressure from the inside relative to the outside. In fact, if you would seal your bottle at sea level, and then take it in an unpressurized environment up to 35,000 feet, I believe at some point it would succumb to the increasing relative pressure on the its inside and burst with much fanfare. I could be wrong though. I also could be wrong on the exact altitudes and pressures, but I believe the basic method is in use.
~KK