What type of wall would make the best soundproof for room?

It depends, How big is the room. If it was me i would put "High density foam pads" all over the walls in the room, and that would get rid of some sound but put Drywall, or Plasterboard behind the foam pads. That should hopefully get rid of the sound from outside the room, and stop any noise in the background, if your using a mic, for example, a Youtube channel, or Twitch treaming channel. Hope this helps. BYE!! 

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