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In camping, a sleeping pad, sleeping mat or ground pad is a simple device often used in conjunction with a sleeping bag. Its purpose is to provide padding and thermal insulation. The ground may become quite cold at night, and is often covered with sticks, small rocks, and other objects that may make sleep difficult. A sleeping bag does not provide adequate protection against either hazard, but a sleeping pad does.
The simplest sleeping pads are sheets of foam rubber or a reflective metallized plastic material, rolled up or folded for storage. The latter provides little extra comfort, but gives good insulation. It is popular because of its low mass and volume. More expensive, and heavier, inflatable models are designed with interconnected air cells that may be compressed for maximum compactness, or inflated through a valve for maximum padding.
Source: en.wikipedia.org

Indoor sleeping bags, sometimes called slumber bags, are widely available, often for use particularly by children. These are usually not designed to be weatherproof, and are often made of natural fabrics instead of the synthetic fabrics commonly used for outdoor sleeping bags. Children’s sleeping bags in particular often feature elaborate, brightly-colored printed designs, such as images of popular media characters. Slumber bags make floor sleeping more comfortable, and are often used for sleepovers, family visits, and other situations where there aren’t enough beds for everyone.Somebody in a sleeping bag

Many different insulating materials are available for sleeping bags. Avid outdoorsmen usually prefer either synthetic fill or down, and they have debated the merits of these materials for years.
Synthetic fill does not readily absorb water, dries easily, and provides some warmth even when thoroughly soaked. These properties may save the owner’s life if, for example, the sleeping bag is accidentally dropped into water on a cold day. Synthetic material is also firm and resilient, so it insulates well even underneath a person’s weight. Synthetics also have the ability to loft faster than down, allowing the sleeping bag to provide the insulation faster than a down bag. On the flipside, synthetic fill cannot be compressed as much as down, causing such bags to take up more space when not in use.
Source: en.wikipedia.org