An Introduction to Zoned Construction
This third method of construction uses different materials or levels of firmness in different parts or "zones" of a mattress support layer. It is also a way of combining comfort ( spinal alignment) in a single layer similar to a progressive construction. While it is often used in more "difficult" circumstances, some zoning schemes are poorly thought out in manufacturing or poorly understood by the person selling them and "suggested" when they are not appropriate. In these cases they they can do more harm than good. Some zoning schemes are also so similar in ILD or firmness between zones that they are not as effective as a higher quality material without zoning. While zoning when done correctly can be very beneficial, it is also the subject of some misinformation and deceptive sales practices which are used to sell mattresses. If you choose a zoned mattress, 2 or 3 zones are generally the most important, and more than this can have questionable benefits and can sometimes lead to the purchase of an inappropriate and very uncomfortable mattress.
Why are some mattresses zoned?
The reason for zoning is because of the difference in weight, thickness/thinness, and surface area of three main areas of the body that are the most difficult to accommodate. The first of these is the hip/pelvic area which carries the greatest amount of weight and has the greatest density, no matter what type of body you have, and often has a wider profile (especially in women). The second is the waist/lumbar area which is often lighter and thinner and has a lower density. The third is the shoulder/chest area. The shoulders are narrower and have less surface area (on the side) and will sink in more easily until they reach the torso which is often wider than the hips but lighter and lower density. Dealing with these 3 areas in all the different sleeping positions and differences in body profiles and the difficulties associated with balancing them in terms of pressure relief and alignment is the reason that zoning is sometimes used in more difficult or extreme body weights or profiles. It is appropriate and can be very helpful when a progressive or differential method of construction cannot accommodate the circumstances.
The various mattress zoning options:
Three-Zone Mattresses
Three-zone mattresses with a firmer layer in the middle under the lumbar and pelvis and 2 softer zones above and below this.
This is most commonly used to help correct alignment and is the most common type of zoning you will see. It uses "normal" ILD's in a support layer with the exception of a firmer layer in the middle. It is most useful when everything is fine in terms of pressure relief and support in all areas of the body except the hips are sinking in too deeply. This is usually a body profile with thinner and relatively heavier hips. This can be very beneficial since the hip area is the heaviest of the body and if they are thinner and the support layers are soft enough to allow the wider shoulders to sink down into alignment, then the hips in turn may easily sink down too far for correct alignment. Men in particular with wider shoulders and chests than hips may do well with this. Those with wider hips but more normal weight will likely not do well with this zoning scheme as their hips need to sink down further in proportion to the shoulder to accommodate their width and help with alignment.
This type of zoning is used to give better support to the lumbar and pelvic area.