Eli5 Why is the soundproofing that is used foam-like materials instead of dense materials?

Question

Eli5 Why is the soundproofing that is used foam-like materials instead of dense materials?

In: Other

Answer 1

Well if you want a simple image of materials, then at small scale, they are like bouncy balls connected via springs.

If you have a solid chunk of material, the sound vibrations can spread straight through it.

Foam is mostly empty space and the material in it is thin zig-zagging pillars. Thus the vibration has to take looong detour, and in the direction changes it bounces back and forth spreading out and the sharp back and forth wobble pattern becomes more spread out and less and less recognizable.