A sofa bed or sofa-bed is typically a sofa or couch that, underneath its seating cushions, hides a metal frame and thin mattress that can be unfolded or opened up to make a bed. A western-style futon differs from a sofabed, although sofa beds using futon mattresses are common.
History
took out a patent for making the first "folding bed" on 18 July 1899. The metal bed frame was capable of being folded, bent mattress closed for use if needed. Later, it was known as a "hide-a-bed". William Lawrence Murphy took out a patent for making "In-A-Dor bed", which is known as a “Murphy bed” today. It is characterized with the folded space-saver into a wall-closet. In 1931, Bernard Castro made and sold the "Castro convertible" by using $400 from his savings. Castro’s design is considered to be the evolution of most sofa beds sold nowadays. After mimicking the Japanese founders, the futon appeared in the United States around 1980. William Brouwer is the person who evolved the first sofa convertible frame style in the United States.
Mattress types
Although most sofa beds use a queen short mattress measuring 60" × 72", other common sizes include 58" × 72", 54" × 72", and 52" × 72". The average sofa bed mattress thickness is 4.5", thus being half as thick as a good standard mattress. Sofa mattresses can be produced out of many different materials, the majority on the market being made of springs or foam.
Spring sofa mattress
Although springs can make a satisfactory sofa bed mattress, the following aspects have to be considered regarding a spring sofa mattress:
Solid height is the length of a compression, when the spring has been deflected enough to allow each adjacent coil to touch each other.
Working length represents the difference between the free length and the solid height.
Active coils is the number of coils that are free to deflect under load, i.e. the total number of coils minus the number of closed coils forming the ends is a measure of the spring quality. The more active coils a mattress has, the less working length it has, which means that the springs are the less likely to deteriorate.
Hydrogen embrittlement represents the hydrogen absorbed in electroplating of carbon steels causing the spring material to become brittle, leading to cracking and spring failure. Plated springs are a problem, and unplated springs are more likely to rust. Plastic coating is an alternative, but is extremely expensive.
The best springs are stress relieved, which means that the springs were treated at a temperature so as to relieve stresses. Not going through such a procedure might cause mattress failure. Unfortunately, many mattress springs are not stress relieved because it is expensive.
Foam sofa mattress
Quality foam sofa bed mattresses compress as needed, the foam acting like an infinite number of springs. A high quality foam gives better support, molds to the body and snaps back to shape. Consider the following factors of a high quality sofa bed mattress:
Density is a measurement of the pounds of polyurethane foam per cubic foot. High density foams can be made very soft, whereas low density foams can be made very firm.
Indentation force deflection is the measure of the foam’s support, representing the pounds of force required to indent a foam sample by a specified percentage of its original thickness. Support is the foam’s ability to "push back" against your body weight, and prevent the foam from "bottoming out" on the frame or base.
Foam durability, flex fatigue and compression set are other terms related to foam performance.
Pocket-coil mattress
Pocket-coil mattresses are generally higher in quality than spring or foam mattresses. Each coil is encased in its own pocket, allowing the mattress to keep its shape over time while also providing more sleep support. Pocket-coil mattresses are thicker than standard sofa bed mattresses, starting from 7" and going up to 10" for a premium product. The high-quality support provided eliminates the need for extra cushioning, allowing the mattress to become the seat of the sofa. This has resulted in a new style of sofa bed that does not require its mattress to be folded up and tucked inside.
