Roofing underlayment is a protective layer installed beneath roofing materials, such as shingles or tiles. It serves as a barrier against moisture, preventing water from seeping into the roof structure. This helps to protect the underlying wood and insulation from damage caused by leaks or condensation. There are different types of underlayment, including felt paper and synthetic underlayment. Felt paper is made from recycled paper and is often coated with asphalt for added water resistance. Synthetic underlayment, on the other hand, is made from polymers and is typically lighter and more durable, offering better protection against the elements.