Expect body impressions. Many of Today's top-quality mattress use extra-plush foams and fibers to create comfort layers designed to cradle your body and relieve pressure. After the first few weeks you sleep on your new mattress with these extra comfort layers, you will likely notice some body impressions. Body impressions, often referred to as body signatures, are where the mattress has slight indentions where you lie at night, on the surface.
These impressions are normal. They indicate that the comfort layers are conforming to your body, as they are supposed to do, and shouldn't be considered a sign that something is wrong with your new mattress.
King and queen size beds often develop a hump in the middle of the mattress where no one sleeps. This is very normal and not at all considered a defect. Your mattress will naturally remain firmer where you and/or your partner don't sleep. If you and/or your partner do not sleep in the center of your bed, the center will remain firmer than the sides where you do sleep.
Here is a diagram depicting what is considered to be normal, and what is not normal:
If your body impression or the entire mattress is sagging 1 ½" or greater on an inner spring, or ½" on memory foam, there is a problem. Contact the manufacturer to ask about filing a warranty claim if you are still within the mattress warranty period.
There are a few things you can do to improve the longevity of your mattress. Rotate your bed head to foot. We recommend doing this every few weeks for the first few months, and then once with the seasons. It is also a good idea to take naps, or snuggle with your family in the center of the bed as frequently as possible. This will allow for even wear of the mattress. Also, make sure you have a solid support system for your bed such as The Bed Beam or the Elm-211. A queen or king size mattress set without a proper center support will sag very quickly, and this will not be covered under your warranty. A few of my suppliers have added a center support requirement for their twin and full size mattresses. Check your warranty and make sure you're protected.
Always protect your mattress with a stain and water resistant mattress protector, like the Serta Sleep-to-Go Elite Protector. A small amount of liquid, even body sweat, has the potential to break down the foams in your mattress. This destroys the foams and leads to excessive body impressions. Although body impressions may be unsightly to some, unless they are deeper than the warranty allows and causing discomfort, they're harmless to you and your bed.