Except the cells are formed with rigid members which transmit sound (and heat) quite efficiently. Sound isolation can't just be done with mass. There has to be

Except the cells are formed with rigid members which transmit sound (and heat) quite efficiently. Sound isolation can't just be done with mass. There has to be a decoupling you can't get with a brick wall alone. Even advanced heating/cooling efficiency techniques with wood framed houses involve some form of isolation - no single material will exist all the way through the wall. They're decoupled with several inches of foam. Even modern studs are being built in a way to minimize the ability for them to transfer heat (Tstuds).