Rockwool One of the growing media that is often used in hydroponic farming systems. What you need to pay attention to is the ability of rockwool to absorb water. A good rockwool is one that easily absorbs water and can store water well. Rockwool is a building material that is used as a material for insulation of rooms or buildings, be it a residential or commercial building from noise. Not only used as a material used for sound insulation, rockwool can also insulate heat and humidity in the room.