UMATHT stands for User Material Heat Transfer. This subroutine is used to define a material's thermal behavior. When you have a thermal analysis and want to define the material's behavior and properties, which the Abaqus CAE cannot support, you need to use the UMATHT subroutine. This subroutine needs to define different variables, including the internal thermal energy per unit mass, the variation of internal thermal energy per unit mass with respect to temperature, etc. In this package, you will learn what the UMATHT subroutine is? When do we need to use it? And how it works, with some examples.