The top is made out of canvas. The bottom is made out of springs.

Trampolines:

I mean the big ones, those ten-by-twelve sheets of unraveling, ripped black canvas stretched taut across a bed of rusted aluminum springs that creaked and groaned, the edges covered by blue tarpaulin, the interior littered with pine straw and the odd bird shit. If you were visiting a friend and they had a trampoline, then like it or not, time was spent on the trampoline. Owners of trampolines had a certain unmistakable attitude when on or around the trampoline itself, that air of a doctor in the E.R, a judge in his courtroom, a dragon in his cave: Authority. There were house rules (these varied: no more than one/two on the trampoline at a time, no back flips, no wrestling) that were laid out with just a hint of "if you were a little smarter, I wouldn't have to tell you this, but then if you were a little smarter you'd have your OWN trampoline." It was also the host's call as to whether a game was to be played, and if so, what game? Popcorn? Bouncing Contest? Wrestling? Mortal Kombat Fight? Cuss Words? At the core of every game was that metronomical bouncing and a disregard for safety. At the apex of a bounce a child is often a dozen feet in the air, and children are notoriously clumsy. The rim of a trampoline is steel, and, failing to hit that, there's always the ground. Another possibility is that a spring, rusty from exposure to the rain, will break and tear through the canvas and a bare foot or hand. But oh, that feeling of effortless almost-flight, the wonderful, simple joy of free-fall, it's worth it, dear God, it's worth every danger.

Trampolines: 17/20. Like all intensely pleasurable experiences, it carries with it no small risk. Unlike many intensely pleasurable experiences, it's worth it.