Thermal mass and insulation are not the same concept. For example, if the environment is continuously hot or cold, thermal mass has no impact while insulation

Thermal mass and insulation are not the same concept. For example, if the environment is continuously hot or cold, thermal mass has no impact while insulation still does. This is most apparent during winter in a cold place, where the environment is always colder than you want the interior, and so thermal mass does not help. R and U values measure only insulation, not mass.