Why is soap foam so good at blocking sound although it is mostly just air?

Question

I have noticed this while bathing when soap foam went into my ears and it almost completely blocked the outside sound. This seems weird as soap foam is just all air with some liquid

In: 18

Answer 1

Every time sound changes what substance it’s passing through, some of it is lost and some of it turns backwards.

For instance think of sound echoing off walls in a cave – some of the sound has gone into the wall, but a lot has come right back at the source.

In a foam a straight line goes “soap, air, soap, air, soap, air, soap, air, soap, air, soap, air, soap, air, soap, air” and at every comma in that list some of the sound is being lost.