Why Do Mattresses Sag?

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If you wake up sore every morning and you feel as though you tossed and turned all night long, a sagging mattress could be to blame. From the inner structure to improper use and care, there are many reasons for mattresses to sag prematurely. Understanding the causes will help you keep your bed in good condition longer.

Box Spring

A common reason for a sagging mattress is actually due to either not using a box spring or having an old worn-out one. It is not just used for extra height, but rather it protects the interior of the mattress. It provides support for the internal structure of the mattress so the whole bed can hold more weight. Without a box spring in good condition, an innerspring mattress will prematurely sag.


The springs inside a mattress are what give it support and structure. If the springs, or coils, are made of thin or weak metal, they will wear out quickly and lose their ability to support the weight of your body. Some mattresses have strong springs but do not have enough to support weight between each one. The springs should also have good quality connecting wires. If there are not enough of these connections, the mattress will sag prematurely.


You must give a mattress proper care and maintenance to prevent sagging. If it is subject to the same sleeping position and weight distribution every night, it will naturally wear in only one area. To combat this, rotate and flip your mattress two or three times a year. Many mattresses currently available are one-sided and cannot be flipped. If you have one of these, rotate it a few times a year to evenly wear the mattress support structure and padding.

Sitting on the Edge

Sitting on the edge of a mattress is a sure way to cause sagging. Most beds are reinforced with an integrated support structure around the edge, but it will be stressed and wear out if you sit on the edge, causing both the edge and the inner support to wear improperly and begin to sag. Instead of sitting on the bed, add a comfortable seat or ottoman nearby to sit down on.


Even if you have a good box spring, you flip and rotate your mattress and you don't sit on the edge, the mattress can still sag if the frame does not provide adequate support. Some beds are supported by wooden slats beneath the mattress. If there is too much space between each slat, the mattress will press between the slats and begin to sag. If there are only a couple of slats, add some extra supports every 12 to 18 inches to keep your mattress from sagging.

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