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Why Is There a Rise in the Middle of My King Size Bed?

Tracey Sandilands

When your king size bed develops a rise in the middle, your sleep may be disturbed by the sensation of “rolling down the hill” toward the edge of the bed where a hollow has formed. Called the “trench” effect, this can occur in the center of a bed that usually accommodates a single sleeper or on both sides of a bed that accommodates two. The trench effect on two sides results in a rise in the middle.


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Pillow Sham

Every sleeper causes body impressions in a mattress. On a new king size mattress, you can sleep in almost any position without a problem, but in a relatively short time, the mattress begins to conform to the impression of the sleepers’ bodies. On a mattress used by two sleepers, hollows develop in the common body positions. If these hollows are more than a foot apart, the pressure pushes the mattress materials towards the center of the bed, creating the rise.


You can prevent the development of the trench effect by changing your sleeping position regularly, especially during the first few months of the life of the mattress. This will help the mattress filling settle evenly and prevent the development of rises and hollows. In addition, adjust the position of the twin box springs underneath the mattress every week or two, moving them a couple of inches apart to prevent upward pressure from the two border rods where they meet in the center.


Mattress rotation is an important aspect of mattress maintenance. While various finished product sizes are available, the standard king size mattress is 76 inches by 80 inches, which is almost square. This makes it possible to rotate the king size mattress a quarter-turn, or sideways. The sleepers will then be sleeping “horizontally” across what was previously the top and bottom of the mattress. This will help to flatten the rise, as the buttocks -- the heaviest area of the body -- will rest on the rise in the middle.

Ongoing Maintenance

Rotate the mattress and adjust the box springs back and forth regularly during the lifetime of the mattress. Protect the top layer of mattress filling by using a mattress pad, which helps to absorb the pressure of the bodies and keeps the mattress clean. Vacuum the mattress surfaces frequently to prevent the buildup of dust in the filler materials, because the weight of dust can also contribute to the settling of the filling in undesirable positions, which may result in a rise in the middle.