MATTRESS SPRING：continual spring
Early mattresses contained a variety of natural materials including straw, feathers or horse hair. In the first half of the 20th century, a typical mattress sold in North America had an innerspring core and cotton batting or fiberfill. Modern mattresses usually contain either an inner spring core or materials such as latex, viscoelastic or other flexible polyurethane foams. Other fill components include insulator pads over the coils that prevent the bed’s upholstery layers from cupping down into the innerspring, as well as polyester fiberfill in the bed’s top upholstery layers. In 1899 James Marshall introduced the first individually wrapped pocketed spring coil mattress now commonly known as Marshall coils.
In North America the typical mattress sold today is an innerspring; however there is increasing interest in all-foam beds and so-called hybrid beds, which include both an innerspring and high-end foams such as visco-elastic or latex in the comfort layers. In Europe, polyurethane foam cores and latex cores have long been popular and make up a much larger proportion of the mattresses sold.