Assuming your mattress is placed upon a flat and firm surface, you can get a sag in a memory foam mattress using a lower-quality (lower density) and/or lower ILD (softer) polyurethane foam core. You'd probably be surprised at the poor quality foam used in some very expensive memory foam mattresses. Start looking from the ground up, making sure your bed frame uses a proper center support and go from there. If everything looks good, contact your retailer for further advice and to schedule an inspection.

It is common for mattresses made from polyurethane foam to break down. Check your center support under the mattress. For a queen you should have one and king should be two. Make sure you have proper foundation that it is not sagging. You can run a plumb line across it.

Hi Robert,

There are so many types and qualities of memory foam that it is impossible to say without knowing what type and the density of the foam. No, it is not common for a good quality, high density foam to sag prematurely. If you have it for a long period of time, unprotected, on a broken down frame or box spring...those could be factors that would cause it to sag long term.

Robert, you're operating under the assumption that you bought a good mattress. I'm sure that's what the salesman told you. In fact, visco-elastic memory foam is the worst material ever invented for use in or as a mattress. Besides losing it's resiliency quickly, it sleeps hot, and off-gasses the toxic chemicals it's made from. It's a big money maker for the mattress industry, but the worst choice you can make, as a consumer.

Sagging or "body impression" allowances (or what your manufacturer considers allowable) vary from company to company. The industry norm is 1.5 to 2 inches. Some companies (Tempur Pedic for example) allow only 3/4 of an inch. Do make sure that the mattress is amply supported as has been mentioned. With proper support of a good product, sagging is not the norm. I'm sorry to say there are good and bad qualities in every industry.

It's all about the science and how the mattress is made. Did you know memory foam mattresses aren't memory foam all the way through? It's just the top layer. Memory foam feels kinda like play dough, it won't take a body impression. But, when the polyurethane foam base underneath starts to break down you are going to feel it. Take a look at how your mattress is made and you will see the layers of polyurethane foam and memory foam is just the top layer.

Since the top layer of memory foam doesn't take a body impression no one has to honor 3/4" body impression for their warranty because the memory foam on top is hiding the fact the polyurethane foam base has broken down. The same goes for latex mattresses, I wouldn't buy a latex mattress with a polyurethane foam base or synthetic latex because of the bonding agents make it break down quicker.

There is a video about it on my web-site, Mountain Air Organic Beds dot com, under organic mattresses. You will learn why mattresses don't last and the key to buying one that does.