A good mattress provides comfort and proper support for your back by conforming to your unique body shape. Given that people usually sleep in the same area of the mattress every night, the foams are continually compressed in the same area. Within two or three nights of compression a small indentation will form on the mattress, also known as a body impression. Body impressions are clinically proven to help support spinal alignment and provide the pressure relief needed for a great night’s sleep.
A good body impression enables the bed to cradle your sleeping form gently to provide optimal comfort and posturizing support as shown in the bed above. Ideally, the upper comfort layers of your bed will soften over time to fit your body just right. As the mattress fills into the natural curves of your body, you may notice a mild “dip” in the surface of the bed. Ideally, the upper comfort layers of your bed will soften over time to fit your body just right. As the mattress fills into the natural curves of your body, you may notice a mild “dip” in the surface of the bed. Many people can mistake this impression or dip as a defect in the mattress (i.e. sagging). If your mattress shows and indentation of up to 2 inches this is not a defect; it is the fibers and foam compressing and conforming to your body.
Initially, when you purchase a new bed, you may notice the new mattress feels firmer than it did in the store. This is due to the fact that the upper layers are new and still need some time to “break in” to your natural form. It may be that the bed is new and has not yet obtained a body impression or the bed may be too firm.
Body impressions are similar to the process of breaking in a pair of new shoes. When you wear a new pair of shoes the soles are initially stiff and straight which often causes discomfort. As you continue to walk in the shoes the soles begin to conform to fit the natural curve and shape of your feet which results in a more comfortable fit. Similarly, a good mattress will conform to your unique body shape!
Mattress sag is not good for your sleep or your body. A mattress with sag will collapse in the center and does not provide the proper support needed for comfortable sleep.
Related article: How To Measure Mattress Dip or Sag