Create a new material (Tools -> Edit Libraries -> Materials, press "Add Material" at the bottom). A window will pop up with the various properties. Select the drop down menu for the relevant items in the "Type" column, the default is "Simple" -- you want "Tensor".
Create a new material (Tools -> Edit Libraries -> Materials, press "Add Material" at the bottom). A window will pop up with the various properties. Select the drop down menu for the relevant items in the "Type" column, the default is "Simple" -- you want "Tensor".