Hi Richard,

Once the material is created in the Panels Materials lib select the part you want to change and in the Properties list, beside the Material  click the down arrow. 

In the materials list, select the new material for you panel.

If you use the new Quick Design libs, no need to create a new material, you don’t even have to select the part, just open the Panels Materials and select the part name and change its thickness.

You can change the thickness, (or any other aspect) of several parts by multi-selecting using the Shift or Ctrl key.

Below I’ve selected all the outer carcass panels, and can now use the Thickness box to change  all these panels.

All the best,

Ness