camping Camping is a form of outdoor recreation or outdoor education involving overnight stays with a basic temporary shelter such as a tent. Camping can also include a recreational vehicle, sheltered cabins, a permanent tent, a shelter such as a Bivy bag ...

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

. 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 temperature ...

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 Insulator may refer to: * Insulator (electricity), a substance that resists electricity ** Pin insulator, a device that isolates a wire from a physical support such as a pin on a utility pole ** Strain insulator, a device that is designed to work ...

Types

Manually inflated

Closely related to the

air mattress An air mattress or airbed 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 and South Africa, is called a lilo ("Li-lo" being a gene ...

, 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 and ...

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 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 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 ...

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 EN 13537 (or EN13537) is a European standard designed to standardize the temperature ratings on sleeping bags manufactured and/or sold in Europe. As of 1 January 2005 a CEN criterion came into effect covering the testing and publication of tempe ...

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

, 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 aggregate bound together with a fluid cement that cures to a solid over time. It is the second-most-used substance (after water), the most–widely used building material, and the most-manufactur ...

granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, 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 coo ...

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

snow Snow consists of 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 througho ...

, 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