A special optical property object that allows a user to define their own tables of cross-section with wavelength and temperature. The method ISKOpticalProperty::AddUserDefined is valid for this object and can be used to define tables of absorption (or scattering) cross-sections as a function of wavelength. Each table is specified for a given temperature. Users should ensure the tables span the useful range of wavelengths as cross-sections outside the wavelength ranges are set to zero. Cross-sections requested outside the range of temperatures are truncated to the nearest temperature table.