This is perhaps one of the oldest underlayments used in roofing. It is inexpensive, easy to manufacture, and easy to install. The roofing manufacturer creates this product by embedded asphalt into 15 lb or 30 lb paper. The result is a slip and water resistant underlayment which, like all underlayments, serve as an additional layer of protection against wind driven rain which can get up under shingles. This is the recommended solution for cost effective roofs where you may not be occupying the building for any length of time i.e. you are selling your home.