How do I deselect material in level editor

Sorry if this comes off as a bit stupid but after I selected a material in the content browser it doesn’t seem to want to go away. Whenever I create a new bsp in the level editor all it’s faces automatically gain the last material I selected. How do I prevent it from loading a material on new bsp’s? I’ve already tried unselecting it but that doesn’t seem to help. I did exit the editor and load back in and that solved the problem, however I’d like to deselect without having to do that every time.