Inner Spring Mattresses are by far the most popular type of mattress. Over 80% of mattress sets sold today are in this category. They can range from very inexpensive sets designed for children or light duty usage to ultra-luxury sets that have plush pillowtops, wrapped coils, and 10-15 year warranties.
Innerspring mattresses have wire coils as the support structure. An innerspring mattress has a strong border wire attached to the perimeter of the coils. The border wire supports the coils, helping to retain shape and reduce sagging. The edge is reinforced with specially shaped springs or foam to support the sleep surface right to the edge, to help prevent 'rollout' and edge breakdown. The upholstery is separated from the innerspring system by an insulator, a tough padding, wire or netting layer that prevents the upholstery from sinking into the coils.
Innerspring Support System
Number of Coils
The way that the coils are constructed is the main factor in determining the amount of support the user gets. The number of coils is not longer considered the "best guage" of the quality of a mattress.
This all depends on the mattress size, but mattresses generally come with 300 to 800 coils. Based on a queen-size mattress, 500 to 800 coils is considered firm. However, some of the best and most comfortable mattresses only have around 400 coils, and even fewer in a full mattress will provide decent support. This can impacted by the use of a heavier gauge wire, therefore adding more steel to the mattress.
There are a number of misconceptions with regards to coil count and firmness. Doctors once said that firmer mattresses give better support. This was actually only true with a small percentage of people who sleep on their backs and/or stomachs. Research shows that most people sleep on their sides. The side of the human body is not flat (like a back,) and a mattress that conforms better to the body and gives better support putting the spine into proper alignment or it's natural resting position has proven to be better. Individually wrapped coils have proven to be the best factor in support for side sleepers.
Coil Gauge
The heavier gauge (thicker wire) coils would offer a greater deal of support than lighter gauge coils. It has been proven that this is not true and some mattress manufacturers compensate for thinner gauge steel wire by increasing the coil count and specifying the type of coil.
Low coil counts and heavy gauge wires can seem firm in the store, but it is likely that such a mattress will not hold up long because it simply does not have enough coils.
Premium mattresses feature 13.75-gauge (1.63 mm) coils. Coils are measured in quarter increments. The lower the number, the larger the diameter of the spring. With coils in the 14 to 15.5 (1.63 to 1.37 mm) gauge range, it is important that the total coil count be high the coils would otherwise give easily under pressure.
A 12.5 gauge (1.94 mm) innerspring coil, the thickest typically available, may feel rock hard in a double mattress even with a coil count of 400 or less.
