Saturated felt is a type of felt with a paper-like consistency manufactured by saturating felt with asphalt to add water-resistant qualities.
Through the process of saturating the felt paper with asphalt, saturated felt becomes extremely resistant to moisture. For this reason, saturated felt is used in a number of different applications. The most common uses of saturated felt are as a floor underlayment and in roof installation.
Using a saturated felt underlayment for floors helps to ensure a better installation of wood paneling and helps to prevent moisture from the ground flowing up to the flooring. This is especially important when dealing with wood flooring due to its sensitivity to moisture, especially on its lower half which cannot be treated following installation.
Saturated felt is used frequently when installing roofs to offer a better surface for nailing the shingles into the plywood roof and to provide temporary moisture protection to the underlying plywood surface during the installation process which can span a several day period.