Flooring underlayment is a layer of material that is installed between the subfloor and the flooring surface. It is typically used to provide cushioning, sound reduction, and moisture protection, and to improve the durability and longevity of the flooring. Underlayment materials can include foam, cork, rubber, and other synthetic materials. The type of underlayment chosen will depend on the type of flooring being installed, as well as the specific needs and requirements of the space. Proper installation of flooring underlayment is crucial for ensuring a successful and long-lasting flooring project.