If you’ve been in the construction industry long enough, chances are you’ve had to remove an old mineral wool insulation product during a renovation. I know I have. It’s itchy, easily falls apart, and it often doesn’t completely fill a cavity bay. I’ve had many conversations with other builders who will not consider using a mineral wool product because of their past experiences with the older mineral wool insulations. I can tell you; the old stuff is nothing like modern stone wool.
Heat wants to move from someplace hot to someplace cold. It’s desire to reach equilibrium is one of the principles of the second law of thermodynamics. We have many methods and materials we use in construction to try to slow this movement. It’s expensive to condition a space and we want to hold on that space conditioning for as long as possible. One way we try to slow heat loss or gain is to prevent the wind from blowing through the home. Another is to shade the sun from beating through a window on a hot, sunny day (in some climates at certain times of the year, the sun can be a blessing). Insulation is one of the big ones we use to provide comfort to homeowners.