Ludwig Bertalanffy describes two types of systems: open systems and closed systems. The open systems are systems that allow interactions between their internal elements and the environment. An open system is defined as a “system in exchange of matter with its environment, presenting import and export, building-up and breaking-down of its material components.” Closed systems, on the other hand, are held to be isolated from their environment. Equilibrium thermodynamics, for example, is a field of study that applies to closed systems.