On the material edit view you can also give the material a category. This is usefull for keeping your materials grouped together by a common type and makes the material view more organized. Just tap the category button to add, edit or choose a category. Basically the view will let you pick a category and switches back to the material. But you can add a new category with the + sign in the upper right corner or choose "Edit" to switch to edit mode. In edit mode you can now tap a category and edit its name. For your convenience, you can tap the "Done" button on your keyboard to get back when you are finished. One thing to note: you can't delete the standard category.