>"but isn’t the last layer a real pain to get off when you have to rip it off your arm hair?"
Ah, but that is also weight-saving. I can leave my razor at home.
For the younger set. Just a few years ago, at your 5th birthday party, you used one of these party favors:
When the air pressure inside the coiled tube is low, the coil is contracted. When the air pressure is greater inside the coiled tube, it expands (you blow in it, it moves).
If you made such a coiled tube out of metal, sealed some air inside and through gears magnified that movement to move a needle around on a dial, you'd have created an altimeter. These Thommen alitmeters are graduated in 20-foot intervals, but you can read them to 5 feet. They are sensitive enough that I can see the needle move if I crack the car windows as I'm driving down the road.
I always wanted to create an altimeter using an expanding bag of Cheetios, inside a cigar box, pushing a paper clip of the box (which would be calibrated in feet of altitude) with a rubber band to return the needle upon descent. Then the Unabomber came on the scene, caused many of us at UC Berkeley delays for security at the computer science building, and increased the suspicions about home-made pressure switches.