The design and manufacturing processes for mattresses has changed dramatically over the years thanks mainly to advances in material technology. Old-fashioned mattresses were little more than springs covered by a thick material layer; now there are thousands of different variations on size, material and spring design. These are often referred to as the mattress grade, but are usually calculated separately allowing for a considered consumer choice.
Mattresses consist of many layers of different materials, each selected because of their properties relating to the mattress. Most mattresses have between three and eight layers. The grade in this sense refers to the quality of the material used in constructing these layers. The most commonly used in high-grade mattresses are wool, silk and memory foam, as these offer a good balance between softness of the mattress, sturdiness of the design and its ability to mould to the body.
The innerspring coils are the smaller coils contained in the mattress. The more coils there are, the more the mattress will adjust itself to your weight and body shape. Top mattress manufactures only have one grade for the coils, but other companies will vary the grade depending on the quality of the mattress. The grade does, to a great extent, refer to the number of coils; the more coils, the higher the grade, although this is not always true, as the grade also refers to the quality of the metal used, the space between and the durability of the coils.
There are two basic designs for a mattress, box spring or fixed foundation. Box springs act like shock absorbers in a car and are still used by most top mattress manufacturers. As material technology has improved, many companies now use a fixed foundation, which does not include box springs. This is because the layers and the innerspring coils remove the need for extra springs. There is no real grading system on this, but it is a consideration.
The mattress itself can also be made from different materials, separate from those used to form the layers. Some of the most widely advertised are memory foam mattresses, which mould to your shape when you are lying down, but go back to normal when you get out of bed. These are normally made from viscoelastic, which used body heat to change shape, or latex, which does it naturally. There are also pocket spring mattresses, which are far and away the most common. These use small springs sewn into pockets on the top and bottom of the mattress. Each of these springs adjusts itself individually to your body. Memory foam and pocket spring mattresses each have their own grading system based on the material. The more pocket springs or better quality foam, the higher the grade.