Net pots/cups are used for hydroponic systems that have the plant's roots suspended over a nutrient solution. Usually used with aeroponic systems. The Aeroflo and RainForest are examples of aeroponic systems. They are sometimes used with Nutrient Film Systems too. You can fill them with Hydroton clay pellets or the small rockwool cubes. The Hydroton offers both support and excellent aeration for the plants. The pots are plastic with mesh around the edges and across the bottom. The cups measure 2-1/4" across the top and 2" tall. 1-1/2" wide at the base.