If you want to get rid of that material, you have to get rid of the region (the blue area) where that material is in use. To remove that region, you must merge it with the material below, the gypsum board, so that the layer is gypsum board only. To merge it, click on Merge Regions, hover the mouse over the edge between that material and the gypsum, and wait until you see a little arrow with a tooltip that tells you which layer will remain. After that, you should be able to delete that material.
Alfredo Medina _________________________________________________________________ ______
Licensed Architect (Florida) | Freelance Instructor | Profile on Linkedin