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 peat-based media. The properties of Growcubes make it like a 50/50 mix of absorbent to repellent stonewool.