camping Camping is an outdoor activity involving overnight stays away from home, either without shelter or using basic shelter such as a tent, or a recreational vehicle. Typically, participants leave developed areas to spend time outdoors in more nat ...

, a ground pad, sleeping pad, thermal pad, sleeping mat, or roll mat is lightweight pad, common among

hikers Hiking is a long, vigorous walk, usually on trails or footpaths in the countryside. Walking for pleasure developed in Europe during the eighteenth century.AMATO, JOSEPH A. "Mind over Foot: Romantic Walking and Rambling." In ''On Foot: A Histo ...

, backpackers and budget travelers, often used in conjunction with a

sleeping bag A sleeping bag is an insulated covering for a person, essentially a lightweight quilt that can be closed with a zipper or similar means to form a tube, which functions as lightweight, portable bedding in situations where a person is sleeping ...

. Its purpose is to provide padding and

thermal A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...

insulation. All types currently available use air as their primary form of insulation. In its simplest form a sleeping pad consists of a foam-like material that is about half a centimeter thick (about a quarter of an inch). The dimensions of the pad are usually about the same length as a

and a little wider. Slight variations in design can be found, such as rippling in the foam, but these do not significantly affect the pad's thermal properties. A common misconception is that the pads are primarily for creating a more comfortable sleeping or sitting area. Instead, the primary purpose of the pad is to prevent the loss of

body heat Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperatur ...

into the ground while sleeping. The materials used are typically filled with air pockets, slowing down the conduction of heat through the pad, as air is one of the best (and cheapest) insulators.

Types

Manually inflated

Closely related to the

air mattress An air mattress is an inflatable mattress or sleeping pad. Due to its buoyancy, it is also often used as a water toy or flotation device, and in some countries, including the UK, is called a lilo ("Li-lo" being a specific trademark -- derived ...

, a pad of this type requires an external pressure source to inflate, typically in the form of a pump or by blowing orally. Convection of the air inside the mattress reduces the amount of insulation it provides. More complicated mattresses reduce convection by partitioning the internal cavities, or by filling the cavities with material to trap the air such as

down feathers The down of birds is a layer of fine feathers found under the tougher exterior feathers. Very young birds are clad only in down. Powder down is a specialized type of down found only in a few groups of birds. Down is a fine thermal insulator an ...

or synthetic insulation. Manually inflated pads have the advantage of offering good thickness and a great deal of comfort while being lightweight and able to pack to a small size.

Self-inflating

An extension on the conventional manually inflated mattress, this type is capable of self-inflation due to the open-cell foam that fills the internal cavity. For many years this design was protected by various patents held by

Cascade Designs Cascade Designs is an American company specializing in outdoor recreation products. It is located in Seattle, Washington and Reno, Nevada, and was founded in 1972 by two former Boeing engineers, who were avid backpackers. Their first product in ...

and they were an unusual and premium item. But since these patents expired many other manufacturers are now producing this type of mattress and they are now commonplace. These mattresses are lightweight and pack to a small size, which make them popular amongst hikers and campers.

Foam

Closed-cell

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 ...

is used to produce mats that can be used without requiring any inflation. Closed-cell foam pads are lighter and more durable than their self-inflating counterparts, as they are constructed of fewer materials and not susceptible to damage from accidental puncture. Many may also be trimmed to size should the user choose to do so. However, they are generally not as comfortable as manually inflated and self-inflating mats because they are thinner, and may also take up more space in a pack, depending on the materials used. Variations include textured or shaped foam to increase the unrolled volume and/or change the stiffness of the mattress. This can also be used to trap the air within ridges or an egg-carton type of texture. Open-cell foam, although comfortable, is rarely used in the outdoors due to its ability to absorb water (like a sponge) and its air cells are crushed in use reducing its insulation capacity.

Insulation ratings

A sleeping pads's warmth is characterized by R-value. But unlike sleeping bags' EN 13537 test standard and widely accepted recommendations, sleeping pad R-values lacks a simple mapping and label for 'how much warmth' a consumer should expect. Combining various standards and various authors' research, an approximate R-value to temperature chart follows: Same as EN 13537, a "standard man" is assumed to be 25 years old, with a height of 1.73 m and a weight of 73 kg; a "standard woman" is assumed to be 25 years old, with a height of 1.60 m and a weight of 60 kg. The sleeping bag and pad system (above, below, and sides) should provide the same insulation value all around a person, but cost, size, weight, comfort, and lack-of-knowledge often lead persons to reduce the R-value to below their personal 'recommended R-value'. Since the pad and bag work together, a 'warmer' bag can compensate the a 'thin' pad and a 'thick pad' for a 'cold' bag. Highly heat-conductive surfaces (e.g.

concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wid ...

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies un ...

) require more insulation for the same temperature than insulating ground surfaces (e.g.

snow Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughou ...

, dry moss, loose soil, wood, etc.). More heat is lost downward when sleeping on one's stomach vs sleeping one's side (due to reduced contact area and cooler body parts in contact). Most persons can 'feel the cold ground' at approximately half the 'recommended R-values'. Sleeping pads R-values range from 1 to more than 10. A few category examples follow:

References