The advantage of using biomass in the form of a pellet is its energy density. This refers to the amount of energy that can be stored in a given amount of a material. On their own the wood and residues like wood chips and sawdust that make up biomass do not have a high energy density. A kilogram of wood, for example, stores little energy, compared to fuels like coal, diesel or uranium. However, by compressing forest industry residues into a pellet, biomass becomes significantly more energy dense.