A friend recently said to me that she hated opening up her luggage after flying somewhere, only to find that shampoo, moisturizer and the like had leaked out of their bottles, spreading goop of various kinds in her bag. There’s often a way to avoid it.
The basic problem, as most of us know, is that the luggage compartments of most airliners don’t get pressurized to sea level or even the 8,000-foot-ish pressurization we passengers enjoy. The part that most folks don’t get is that gases are affected by pressure, and liquids aren’t.
Thus, if you put a shampoo bottle that’s half full in your checked luggage, it’s half full of liquid shampoo, and half full of gaseous air. The air that expands once the plane’s at 35,000 feet, but the shampoo doesn’t. The expanding air then pushes the shampoo out of the bottle. But if there’s no air in the shampoo bottle, then the changing air pressure outside the bottle doesn’t affect the liquid contents of the bottle, and all of the goop stays in the bottle.
So wherever possible, squeeze your bottles until there’s no air inside, and then cap the bottle, or buy squeezable plastic containers for travel and fill them with the shampoo, moisturizer or whatever before every trip. That’s also why it’s important to squeeze any air out of a ziplock baggie before putting it in checked luggage. Remember: gas expands and contracts under pressure, liquid doesn’t. Happy travels!