Paper cover book, with soft cover or hard cover, is widely applicable for schools and companies, because it is easy and cheap to process. It can be bound in different ways. For the saddle stitched binding, 6 to 12 pieces of A4 paper are stapled in the central line and folded in half. For spiral binding, a spiral wire is looped through large perforations at the top or side of A4 or A8 paper. Additionally, some book covers adopt coating process which makes them resistant to water.