The noise we hear is made by vibrations which transfer through the air or the structures. To prevent these vibrations from entering our home or office, we have to isolate them as much as possible. By using various different approaches it is possible to deter the vibrations and cancel noise from the outside or the room nearby.
Most modern building use soundproofing panels to cancel the noise. These panels are very simple to make - they are basically two planes that form closed space between them. The vibrations, or sound, that attempts to come through them will lose its power somewhere between them. There are no chemicals used here, no special technology, just pure air which is closed with two panels, catching the vibrations and soundproofing a room.
Of course, this approach is also good if you want to keep the sounds in your room. A deaf room, which recording studios use, requires all the sounds to stay within the room in order to record the best possible audio. With soundproofing, the sounds will stay inside the room so that the voices and instruments can be heard clearly. Yes, it's a very different need than from the one mentioned above, but the approach is the same.