A mattress pad is designed to lie atop an existing mattress

Mattress

A mattress is a manufactured product to sleep or lie on, consisting of resilient materials and covered with an outer fabric or ticking. In the developed world it is typically part of a bed set and is placed upon a foundation....

. They are made primarily from foam. Their function is to provide a layer of comfort and warmth between the user and the mattress. They are of particular benefit when the existing mattress is worn or uncomfortable. Toppers quite often have a contoured profile to facilitate airflow. Visco-elastic

Viscoelasticity

Viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials, like honey, resist shear flow and strain linearly with time when a stress is applied. Elastic materials strain instantaneously when stretched and just...

 foam toppers are regularly used in medical institutions because of their pressure relieving properties. The foam used in the construction of these memory foam

Memory foam

Memory foam is polyurethane with additional chemicals increasing its viscosity and density. It is often referred to as "visco-elastic" polyurethane foam, or low-resilience polyurethane foam . Higher-density memory foam softens in reaction to body heat, allowing it to mold to a warm body in a few...

 toppers reacts to both pressure and temperature. This combined with its greater density are properties that give them their characteristic "weightlessness" sensation.

An electric mattress pad is made of heavy fabric with heating filaments woven into it. In the UK, this is called an "electric blanket

Electric blanket

In the US the electric blanket is a blanket with an integrated electrical heating device usually placed above the top bed sheet. In the UK and Commonwealth, electric blanket commonly refers to an electric mattress pad, which is placed below the bottom bed sheet. Electric blankets usually have a...

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