Growcubes are small, loose 1/2" cubes of stonewool. Advantages are better aeration, maximum drainage so that you can hardly ever over-water your plant, easy mixing with other loose media (such as expanded clay rocks or coconut fiber), lightweight and much cleaner than pot-based media. The properties of Growcubes make it like a 50/50 mix of absorbent to repellant stonewool.