I think we have a confusion of terms here. Glass wool does not reflect sound. It is used as acoustic insulation because it absorbs acoustic energy. That’s different from reflection. If you’re in a room whose walls are made of a sound reflecting material, it will be a very noisy room because sounds will keep bouncing around. If the walls are sound absorbing the sound will die when it hits the walls, and the room will be quieter.
Which are you looking for?