Underlay may refer to flooring or roofing materials, bed padding, or a musical notation.

Flooring

Underlay or underlayment"Underlayment." ''The Oxford English Dictionary''. 2nd ed. 1989. generally refers to a thin layer of cushioning made of materials such as

sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through t ...

rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds. Thailand, Malaysia, and ...

foam Foams are materials formed by trapping pockets of gas in a liquid or solid. A bath sponge and the head on a glass of beer are examples of foams. In most foams, the volume of gas is large, with thin films of liquid or solid separating the reg ...

, felt,

crumb rubber Crumb rubber is recycled rubber produced from automotive and truck scrap tires. During the recycling process, steel and tire cord (fluff) are removed, leaving tire rubber with a granular consistency. Continued processing with a granulator or cr ...

, or recycled

plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...

; this material is laid beneath

carpet A carpet is a textile floor covering typically consisting of an upper layer of pile attached to a backing. The pile was traditionally made from wool, but since the 20th century synthetic fibers such as polypropylene, nylon, or polyester hav ...

ing to provide comfort underfoot, to reduce wear on the carpet, and to provide insulation against

sound In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by the ...

moisture Moisture is the presence of a liquid, especially water, often in trace amounts. Small amounts of water may be found, for example, in the air (humidity), in foods, and in some commercial products. Moisture also refers to the amount of water vapo ...

, and

heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...

."Underlay." ''The Oxford English Dictionary''. 2nd ed. 1989. In general, it is a layer which is underneath another layer, so ''underlay'' is thus also used to describe many different surface-covering products. In vinyl flooring or "

linoleum Linoleum, sometimes shortened to lino, is a floor covering made from materials such as solidified linseed oil (linoxyn), Pine Resin, pine resin, ground Cork (material), cork dust, sawdust, and mineral fillers such as calcium carbonate, most com ...

", the underlay is the thin layer of plywood that is fastened over the structural

subfloor A floor is the bottom surface of a room or vehicle. Floors vary from simple dirt in a cave to many layered surfaces made with modern technology. Floors may be stone, wood, bamboo, metal or any other material that can support the expected load ...

to create a uniform, smooth platform for the sheet vinyl. For laminated woo
installation of flooring
the underlay provides a “vapor barrier” to prevent moisture from coming through the floor of the home and then migrating into the flooring; the underlayment may also have noise-dampening properties. A self-leveling underlay is a cement-like product that can be pumped in liquid form onto the floor in order to create a level floor.

Carpet

Popular carpet underlays are * foam rubber * crumb rubber * felt * cork More recent innovations in underlay materials include recycled

underlay, which can be made from plastic bottles and other single-use plastics for reduced environmental impact. Carpet underlays are typically 6-10mm. They primarily provide foot comfort, but they also reduce carpet wear and provide sound and thermal insulation.

Wood floor

Underlay for timber floors is typically 3mm closed cell plastic foam. This primarily provides sound insulation and a vapour barrier.
A watertight vapour barrier should only be used though, when neither

condensation Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapor to ...

from humid air coming from beneath nor water spillage coming from above are to be expected. Especially if there is spillage it will otherwise take a much longer time for the moisture to disperse and evaporate if it is prevented by the barrier from seeping through the wooden flooring. This might make it necessary to raise the temperature of the floor to facilitate evaporation and prevent rot.

Roofing

''Underlay'' is also the term for the material under roofing tiles; this roofing membrane is often made of rubber and is used to seal the roof and prevent leakage. Underlayment used with roofing shingles provides a second layer of water proofing to prevent leaks and is called

tar paper Tar paper is a heavy-duty paper used in construction. Tar paper is made by impregnating paper or fiberglass mat with tar, producing a waterproof material useful for roof construction. Tar paper is distinguished from roofing felt, which is impreg ...

roofing felt Bituminous waterproofing systems are designed to protect residential and commercial buildings. Bitumen (asphalt or coal-tar pitch) is a mixed substance made up of organic liquids that are highly sticky, viscous, and waterproof. These systems ar ...

, or since the 1990s synthetic underlayment. Roofing underlays can be breathable or non-breathable depending on the ventilation requirements of the building.

Bedding

Bedding underlay (or mattress overlay) is a thick, extra layer of padding between the bed mattress and

bedding Bedding, also known as bedclothes or bed linen, is the materials laid above the mattress of a bed for hygiene, warmth, protection of the mattress, and decorative effect. Bedding is the removable and washable portion of a human sleeping environm ...

. Underlays are designed to increase comfort and support, while extending the life of the mattress (or

mattress protector A mattress protector (also mattress cover, mattress pad may mean this or a mattress topper) is an item of removable bedding that sits on top of, or encases, a mattress to protect it. Some mattress protectors also provide protection to the perso ...

). Common underlay materials include:

Wool Wool is the textile fibre obtained from sheep and other mammals, especially goats, rabbits, and camelids. The term may also refer to inorganic materials, such as mineral wool and glass wool, that have properties similar to animal wool. As ...

, foam, and

latex Latex is an emulsion (stable dispersion) of polymer microparticles in water. Latexes are found in nature, but synthetic latexes are common as well. In nature, latex is found as a milky fluid found in 10% of all flowering plants (angiosperms ...

Music

In music, ''underlay'' refers to text intended for vocalization – positioned either directly or indirectly under notes on a musical staff.

References

Rugs and carpets Floors {{furniture-stub