Acoustic panelling , This is made up of lots of small shapes which "brake up" the sound waves and reduce the level of reverb. They are made out of foam that absorbs the soundwaves to make it a rather dry room. It also stops the sound leaking out the room also sound from getting in which could potentially ruin a recording session.

Difference Between Acoustic Treatment & Soundproofing

A acoustic treatment is different from soundproofing, Acoustic treatment reduces the amount of reverb in a environment what gives you a dry or dead as they sound. One of the deadest rooms in the world is called the Anechoic chamber. Some example of a Acoustic treated room would be that it contains acoustic panelling and a acoustic microphone shield. While as soundproofing is materials that either reduce or absorb sound. While sound usually cannot be blocked completely, substantial noise reduction is possible.