In COMSOL Multiphysics, you can use Interpolation, Analytic, and Piecewise Functions to specify a material property.
Interpolation Functions can be used to describe material properties that are defined by a table or file containing values of the function at discrete points. Either enter the data manually or import it from a data file. Then, specify the function behavior between data points and outside of your range of data.
Analytic Functions are used to specify material properties as functions of one or more arguments, or as independent variables, such as temperature or pressure. First, enter the mathematical expression that defines the function. Then, enter the arguments to the function and specify the value range for each argument.
Piecewise Functions are useful for describing a material property that has different definitions on different intervals. You can enter the start and end points for each interval and the function relevant to each interval, as well as choose the interpolation and extrapolation methods.
This video shows you how to create each of these function types for any material property you want.