Mattress coils or also known as mattress springs, are coil springs used in many modern mattresses. A matrix of coils are primarily used to create the bottom section of the mattress. In recent years small "micro-coils" have started being used in the upholstered comfort layer of mattresses, the top layer of the mattress.
Mattress coils were introduced in the mid-late 19th century, and remain popular in the 21st century, particularly in the United States and Asia. In Singapore innerspring mattresses still dominate the market.
There are several types of mattress coils. Coils are popular in mattresses because of its compression behaviour. The firmness as the spring as it is compressed is initially soft, to conform to the body, then hard, to provide support.
Continuous coils is an innerspring configuration in which the rows of coils are formed from a single piece of wire. This is used in lower end mattresses and single mattresses where the isolation of movement is not critical.
Bonnell coils are the oldest and most common. First adapted from buggy seatsprings of the 19th century, they are still prevalent in mid-priced mattresses. Bonnell springs are a knotted, round-top, hourglass-shaped steel wire coil. When laced together with cross wire helicals, these coils form the simplest innerspring unit, also referred to as a Bonnell unit.
Marshall coils, also known as wrapped or encased coils or pocket springs, are thin-gauge, barrel-shaped, knotless coils individually encased in fabric pockets—normally a fabric from man-made, nonwoven fiber. Some manufacturers precompress these coils, which makes the mattress firmer and allows for motion separation between the sides of the bed. As the springs are not wired together, they work more or less independently: the weight on one spring does not affect its neighbours. More than half the consumers who participated in a survey had chosen to buy pocket spring mattresses. Pocketed springs are used in more premium mattresses.