The picture below shows workmen installing cork insulation on the ceiling of the center hall of the third floor for thermal insulation during White House renovations in 1951. Furthermore, Harry Truman chose to renovate the Oval Office during his presidency, incorporating polished cork herringbone floor.
Cork insulation was used heavily in the United States, and was an extremely common choice for buildings until synthetic insulation was invented. At the time, the monetary cost of synthetic insulation was much cheaper and it's negative effects on the environment unknown. It's only fitting that Truman chose cork insulation; it has excellent sound isolation qualities. For a President's important and often times sensitive communications.