Underlayment is a layer of material that sits between the subfloor and the finished floor covering. It provides several benefits, including sound reduction, insulation, moisture protection, and cushioning. Most modern vinyl flooring comes with an attached underlayment or pad, often with a moisture barrier built-in, unless the pad is cork. If the product you choose doesn’t have an attached underlayment, you can almost always install directly over the subfloor without one, but this may result in an unsatisfactory experience. However, underlayment is key if you want to maximize softness, warmth, moisture protection, and noise reduction. The most used types of underlayment for vinyl are cork, foam, felt, rubber, plywood, and OSB. The type of underlayment you should use depends on the subfloor and whether it’s concrete, plywood, or existing flooring material. For example, when installing over a concrete subfloor, a felt underlayment is the best choice, while plywood underlayment is a lot stronger and does better with water. In summary, the type of underlayment you should use depends on the subfloor, the vinyl flooring product, and the benefits you want to achieve.