Many of the pieces of furniture in daily use have spring systems to provide resistance, firmness, comfort, but also mobility to certain types of furniture, such as office chairs. Upholstery springs are found in armchairs, mattresses, chairs, among other furniture where they usually go unnoticed due to the padding that prevents them from sitting.
There are three types of upholstery springs:
- Coil springs. They are coil springs found in antique furniture, but also in high-end modern furniture; its caliber varies depending on the height of the seat, its useful life is very long, as long as the recommendations for use and weight limit are respected.
- Zigzag springs. Also known as sinuous, they are not as durable as coil springs, but being less expensive to produce they are used in most modern furniture; they get their name from zig-zag springs because they have just one band of metal that goes back and forth like a fast sine wave. This type of spring is produced in coils and cut to size, they are attached to the front and back rails of chairs or armchairs and, when joined, are capable of supporting the weight of people sitting on them.
- Marshall springs. They are the ones used in the manufacture of mattresses; they are encased within the fabric so that people do not feel them. When pre-compressed, these springs provide extra firmness to the mattress and allow each side of the bed to be independent of the other, meaning sleepers won't feel their partner's movements.
Upholstery spring gauges range from 8 to 11 inches for coil springs and 8 to 13 inches for zig-zag springs. This range determines the three levels of firmness: soft, regular, and hard. In terms of length, they can be as short as 4¾ inches and as tall as 14 inches, however when they are longer than 10 inches they tend to be unstable and tend to fall over. In the case of coils, the shorter the spring, the larger the gauge.