First patented in 1871, coil spring double mattresses have long been the standard for sleeping comfort. Coil spring mattresses have a core that consists of metal coils that are usually joined together at both the top and bottom to form a grid. The springs are then covered with upholstery materials to create the mattress.
Some coil spring double mattresses have a layer of polyurethane foam over the metal coils and possibly a layer of synthetic or cotton batting. The mattresses is then wrapped in a cloth cover. Most coil spring mattresses feature tufting or buttons that go completely through the mattress to prevent the upholstery materials from slipping off the coils. More expensive coil spring double mattresses have thicker upholstery layers over the coils.
There are several types of coils used in coil spring mattresses. Bonnell coils are the original patented coils and have an hour glass shape. Marshall coils are wrapped in a fabric case and are tempered in most cases. Encased coils are each wrapped separately in a fabric case. Off set coils are designed with a hinged effect which causes them to conform better to the body and continuous or Mira coils have the same hinged effect but are made from a continuous strand of steel wire. Mira coils tend to create more noise than other coil springs.
The upholstery material used in the creation of double mattresses is as important as the springs. Some companies are using natural cotton and wool exclusively in their upholstery. These materials can create problems for those who have allergies to either the materials or to dust. Natural materials are more apt to attract both dust and dust mites than synthetic materials. The outer covers of these mattresses may contain polyester, because polyester adds strength to natural fibers and also adds ease of cleaning. If the upholstery materials are natural the mattress should state the type of materials used.
Most coil spring double mattresses contain a layer of polyurethane foam. Polyurethane is a petrochemical and may off gas, but not to the same extent as a memory foam mattress. Dacron or acrylic batting is wrapped around the springs and the foam and then covered with fabric which may be polyester, or a polyester blend or an all natural fabric. For people with allergies to dust, synthetic materials may be best. For people with chemical sensitivities, natural upholstery materials are most likely the best option.
When shopping for coil spring double mattresses, it is wise to know exactly how the mattresses are made in order to compare their quality. Mattresses are an expensive item and it is best to comparison shop to get the highest quality for the lowest price.