If you know anyone who lives in a condo, they probably have a cork underlayment under all their different flooring types. They may have up to 1/2 inch of the stuff laid down under their finished flooring. This is to stop sound from being transmitted to lower floors, and it acts as a thermal barrier too. You do not want to be heating or cooling your neighbor’s condo. I heard of a guy once who lived in a middle apartment that did not have great insulation. He saved on heat because he turned his furnace down and his neighbors on either side had to turn their furnaces up to stay warm. He got free heat because the walls were not well insulated.
Cork underlayment can work to reduce sound transmission as well as act as a thermal barrier. It is great on floors where heat or cold can be conducted. Cork will not flatten over time. It can be installed under wood floating floors and other flooring surfaces. I wish the first apartments my wife and I lived in had cork under the finished flooring. We lived in some noisy places. People have kids and make noise. TVs today have surround sound. You need much more soundproofing in apartments and condos than you did years ago. There is just way too much electronic noise coming from people’s homes.
You do not notice your own noise. You can have the TV blaring your favorite action movie, but your neighbor is not going to want to hear it. And you are not going to want to hear his Bluegrass music blaring while you are trying to sleep. At least I don’t think you will. The point is that cork used as a soundproofing underlayment can help keep tenant relations a lot more friendly in apartment buildings and condos.