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 layer of cushioning made of materials such as

sponge Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a basal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and a ...

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. Types of polyisoprene ...

foam Foams are two-phase materials science, material systems where a gas is dispersed in a second, non-gaseous material, specifically, in which gas cells are enclosed by a distinct liquid or solid material. Note, this source focuses only on liquid ...

, 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 ...

, or recycled

plastic Plastics are a wide range of synthetic polymers, synthetic or Semisynthesis, semisynthetic materials composed primarily of Polymer, polymers. Their defining characteristic, Plasticity (physics), plasticity, allows them to be Injection moulding ...

; this material is laid beneath

carpet A carpet is a textile floor covering typically consisting of an upper layer of Pile (textile), pile attached to a backing. The pile was traditionally made from wool, but since the 20th century synthetic fiber, synthetic fibres such as polyprop ...

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 br ...

moisture Moisture is the presence of a liquid, especially water, often in trace amounts. Moisture is defined as water in the adsorbed or absorbed phase. Small amounts of water may be found, for example, in the air (humidity), in foods, and in some comme ...

, and

heat In thermodynamics, heat is energy in transfer between a thermodynamic system and its surroundings by such mechanisms as thermal conduction, electromagnetic radiation, and friction, which are microscopic in nature, involving sub-atomic, ato ...

."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 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 commonly on a Hessian fabric, hes ...

", the underlay is the thin layer of plywood that is fastened over the structural subfloor to create a uniform, smooth platform for the sheet vinyl. For laminated wood 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 concrete product that can be pumped in liquid form onto the floor in order to create a level floor.

Carpet Underlay

Popular carpet underlays are * pu foam * 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 6-12 mm thick. They primarily provide foot comfort, but they also reduce carpet wear and provide sound and

thermal insulation Thermal insulation is the reduction of heat transfer (i.e., the transfer of thermal energy between objects of differing temperature) between objects in thermal contact or in range of radiative influence. Thermal insulation can be achieved with s ...

Underfloor Heating Underlay

Underlays are also available for underfloor heating in either central heating pipes or electric applications which allow the heat to transmit through the underlay and carpet. Specialist underlays include ThermalStream which have air perforated holes to allow a faster heat transaction.

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 ...

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, roofing paper, felt paper, underlayment, or roofing tar paper is a heavy-duty paper used in construction. Tar paper is made by impregnating paper with tar, producing a waterproof material useful for roof construction. Tar paper is ...

, roofing felt, 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 called 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 environment ...

. 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 person ...

). Common underlay materials include:

Wool Wool is the textile fiber 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 some properties similar to animal w ...

, foam, and

latex Latex is an emulsion (stable dispersion) of polymer microparticles in water. Latices are found in nature, but synthetic latices are common as well. In nature, latex is found as a wikt:milky, milky fluid, which is present in 10% of all floweri ...

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