Answer:
What is lighter than what it is made of?
I'm not really more than holes tied to more holes. I'm strong as good steel, though not as stiff as a pole.
It happens when something has been cut with H2O.
What instrument can make any sound and be heart, but not touched or seen?
What can be measured but not seen?
You use it between your head and your toes, the more it works the thinner it grows.