Highly combustible materials that leave little residue, such as wood or coal, were thought to be made mostly of phlogiston; non-combustible substances that corrode, such as iron, contained very little.
Stærkt brændbare materialer, der kun efterlader meget få rester, såsom træ eller kul, mentes hovedsageligt at bestå af flogiston; ikke-brændbare materialer, der korroderer, såsom jern, indeholdt derimod meget lidt.