Substrate is comprised of a large number of particles. The particle size distribution defines the substrate's texture. Components such as peat moss, perlite, vermiculite, bark, coir, wood fiber, sand, etc. have particles of different shapes (granular, blocky, prismatic, platy or massive), and the size can be coarse, medium or fine. The size of the particles depends on the nature of each component. The structure of a substrate is determined by the way in which the particles are arranged in the substrate.