An air mattress is an inflatable mattress, usually made of plastic or textile-reinforced plastic or rubber. The deflated mattress can be rolled up or folded and carried or stored relatively easily, making air mattresses a popular choice for camping trips and for temporary bedding at home for guests. They are inflated either orally by blowing into a valve, or with a manual foot-powered or electric pump. Some are even automatically inflating (up to a certain pressure -- usually some manual work is also needed) just by opening the valve.
Lightweight, reduced-size air mattresses specifically intended for camping and backpacking are sometimes called sleeping pads, especially when a layer of foam insulation is added under the air chambers. Better quality air mattresses are constructed of fabric instead of sheet vinyl.
Larger, more elaborate air mattresses ("air beds") have come on the market in recent years that are intended for guest use in the home, or as permanent beds.
Light duty inflatable guest mattresses can be packed into a small space for storage. These are generally made of plastic (polyvinyl chloride, PVC). Some have an electric pump and a firmness controller. Vinyl is far less elastic than rubber (but more elastic than textile-backed rubber -- durability is really about material toughness, not material elasticity) and will eventually fatigue, making vinyl mattresses unsuitable for everyday use. But a vinyl air bed might well be sufficient for several months of frequent use, or years of occasional guest use.
Permanent air beds, designed to take the place of a conventional mattress or waterbed, are often mounted on a special foundation. Other innovations allow for a specific firmness setting to be applied to each half of larger mattresses. Air beds with latex rubber air chambers can last for years in daily use, and typically will have multi-year guarantees. Prices are roughly comparable to good quality coil spring mattresses.
As a water toy
The term air mattress may also refer to a certain inflatable swimming pool toy, which has an air-sac "pillow" and several (usually four or five) tubes running its length. Also called a "lilo" (UK), "pool air mat", "air mat", "pool lounge", or "float(ing) mat(tress)", it is used to recline on the surface of a swimming pool. Although it bears some resemblance to an air mattress, it is typically not built as strong and may not reliably stay inflated all night long, making it impractical for use as a bed.