Underlayment or underlay generally refers to a thin layer of cushioning made of materials such as sponge rubber, foam, felt, combination of foam/filmed, and cork. When choosing an underlayment for your new flooring, it is important to use only the type offered or approved by the manufacturer of your particular flooring choice.
Underlayment is used to absorb some typical minor imperfections in the sub-floor; it helps to deaden sound and slightly softens the feel when walking on the floor.
Underlayment is required for any installation of laminate flooring or engineered wood flooring. Because flooring is installed by a “floated,” or “free-floating,” method, the floor itself is not actually attached to the sub-floor.