Underfelt

Underfelt, in flooring terminology, refers to a cushioning layer laid beneath a carpet, rug, or other floor covering. Its primary functions are to improve comfort underfoot, reduce wear on the carpet, dampen impact sound, and provide some thermal insulation. The term is often used interchangeably with carpet underlay, though product construction and performance can vary.

Materials used for underfelt range from natural to synthetic. Traditional underlays are dense felt made from wool or other natural fibers. Modern options include synthetic underlays such as polyurethane foam, EVA foam, rebond foam, rubber, and bonded or nonwoven fiber felts. Underlays may be sold as single-material sheets or as multi-layer systems combining a fiber layer with a foam or rubber backing. Thickness commonly ranges from about 2 to 12 millimeters, with thicker choices offering better sound reduction.

Installation typically requires a clean, dry subfloor. Underfelt is laid out before the carpet and joined at the seams, often using tape, edge joining, or, depending on the product, adhesives. Some underlays are suitable for use with radiant floor heating, while others are not compatible with certain carpet types or moisture-prone subfloors. Always check manufacturer guidance for subfloor conditions and heating systems.

Benefits include improved comfort, reduced noise transmission between levels, and extended carpet life by minimizing friction and pile deformation. Natural-fiber felts can absorb moisture and support mold growth in damp environments, whereas synthetic underlays generally offer better moisture resistance. Over time, some underlays may compress under heavy traffic, reducing cushioning and requiring replacement.