Rockwool is one of the most common growing media used in hydroponics, being compatible with most hydroponic systems. Primarily composed of granite and limestone, or a mixture of the two, rockwool is melted at high temperature, spun into threads, and then fashioned into cubes/blocks or slabs. Blocks and cubes are usually used for the early stage of growing, whilst slabs are designed for drippers. Rockwool is highly absorbant, ensuring roots get the nutrients they need and a strong oxygen supply. The HydroStore stocks market leaders Grodan rockwool products.