Why New Spring Mattresses Sag and How to Fix in 60 Minutes


I spent my teenage years in an antique bed that still had the original springs in the bed frame. This supported a mattress and I am sure it did a wonderful job about 100 years ago.

But now it was like sleeping in a hammock, which would be fine except that I am a side, face, and back sleeper (flip-flopper) so it did no favors for my back.

A simple wood platform conversion using 2” x 4” lumber and a sheet of 3/4” plywood cured this issue and gave me some insight into the issue.

Mattresses sag due to age, failing box spring, sagging platform slats, and wires, thin coil metal, poor coil metal quality, insufficient coil rotations, incorrect coils installed in all/part of the mattress at the factory, poor quality foam, purchased incorrect firmness, not new, and too fat.

Why do Innerspring Mattresses Sag?

Innerspring mattresses sag because they are designed to fail. Companies would go bankrupt if they built innerspring with thick high-quality steel that lasts 30 years.

Their customers would only buy 1 or 2 mattresses during their lifetime rather than 8-10. An old box spring may also be the cause.

Is it Normal for a new Mattress to Sag?

It is not normal for a new mattress to sag. It usually takes years for this to happen, but some reasons it may occur in a new mattress include:

  1. Age: mattresses are not designed or built to last 20 years, even though many of us try to get that many years out of a mattress. My last mattress, well my ex-wife’s, was more than 13 years old when I last slept in it.

    I am sure she had if for at least five years before that too. We would flip it each month, but hey it is going to start sagging. Metal coils lose their spring in small quantities every year.
  2. Failing box spring: Well, if you bought a new mattress but went cheap and didn’t replace the old worn-out box spring then you deserve what you get, a new sagging mattress.

    The least you can do is spring for a sheet of 3/4” plywood and place it on the failing box spring. Cheap and functional, so now your spouse may stop freaking out on you and you still saved money. Win-win.
  3. Sagging platform slats and wires: If this is the case then just purchase a sheet of 3/4” plywood and cut it to size. Install directly on the slats and you are good to go.

    Springs constructed with narrow gauge metal. There is little difference between the quality of foam mattresses, but there can be a substantial difference in spring and coil quality.
  4. Thin coil metal: Think about the coils on your car made with thick steel coils supporting thousands of pounds. How much weight do you think a Slinky can support?
  5. Poor metal quality constructed with a high percent of cheap allows and less quality steel.
  6. An insufficient number of coil rotations: Having fewer coils per length. Think about it, if you have a spring coiled 50 times per 12 inches it will be very strong.

    The spring would be weak as my willpower to not drink an ice-cold beer on a smoking hot summer day if it only has 5 coils.
  7. Incorrect coils installed in all/part of the mattress at the factory: See the entertaining section “Why is my New Mattress Sinking in the Middle?” Below to see how many ways this can happen.
  8. Poor quality foam: Some dealers require the factory to use the cheapest foam possible so they can set a low price, sell many, and then sit back and count their cash.

    This is not the factory’s fault as they don’t care what materials they use as the manufacturing process is the same for quality or crap materials.

    It is the dealer (get your mind out of the weed gutter) who wants to sling cheap mattresses to unsuspecting buyers.
  9. Purchased incorrect firmness: The mattress is super soft plush and the old one was firm so it appears to sag. I doubt this would happen if you went to a store and tried out mattresses.

    But this can happen if you purchase online and did not research the firmness before you made the purchase. So this one is on you if this is the situation.

    If the mattress is on a box spring you can try the plywood trick for a possible solution. If it is on a solid foundation then you are pretty much fubar if you cannot return the mattress.

    A less desirable solution is to put 1/2” or 5/8” plywood on top of the mattress and add a 4” or 6” foam mattress. I know I know, crappy solution but an option.
  10. Not a new mattress: You were hustled (check the tags for manufacture date). Many discount mattress warehouses are operated and run by crooks.

    Look around the back of the building. You will likely find a couple of workers Cheetching it. Or even just smell the workers as they often reek of Mary Jane.

    I have nothing against Devil’s lettuce, but some do so this is a heads up.

    They are often paid a commission on sales so they may push the most profitable products, and what is more profitable than a returned mattress?
  11. You are too fat. Writing this reminds me to start fasting again starting today 🙁
ImageTitlePricePrimeBuy
Product ImageZinus Annemarie Solid Wood Bed Support Slats / Fabric-Covered / Bunkie Board, QueenPrimeEligibleBuy Now
Product ImageGreaton Heavy Duty 0.75-Inch-Mattress Support Wooden Bunkie Board/Slats, Full, BeigePrimeBuy Now
Product ImageReplacement Support Wooden Slats for Metal Bed Frame Holders Kits Bundles Available in Two Lengths-Cut to The Length of Your Choice (5 Slats Pack) (39.3"X2.08"X0.33")PrimeEligibleBuy Now
Product ImageMayton, 0.75-Inch Heavy Duty Vertical Mattress Support Wooden Bunkie Board/Slats with Cover, Twin, BeigePrimeEligibleBuy Now
Product ImageGlideaway X-Support Bed Frame Support System, GS-3 XS Model - 3 Cross Rails and 3 Legs - Strong Center Support Base for Full, Queen and King Mattress, Box Springs, and Bed FoundationsPrimeBuy Now

Prices pulled from the Amazon Product Advertising API on:

Why is My New Mattress Sinking in the Middle?

A new mattress may be sinking in the middle due to a manufacturer’s defect where they accidentally installed lesser quality springs in the middle of the mattress. This can actually happen quite easily by:

  • the ten-year-old “apprentice” grabbing some wrong springs from inventory.
  • the twelve-year-old inventory Manager storing springs in the wrong location.
  • the spring manufacturer placed springs in an incorrectly labeled box.
  • The eleven-year assembler was up all night with his two colic children and in a zombie trance, he or she somehow installed fewer springs than necessary. Thankfully this possibility is the least likely 😉

One of the cheapest and fastest solutions is to add this cheap unit for about $16 bucks and you can research it more here.

Scott Boyd

Why Does my Mattress Have a Dip?

A mattress may have a dip anywhere in the mattress and it can be small, large, or in various areas throughout the mattress. A potential cause is if the worker at the factory mixed up different length coils such as ten-inch and 11-inch.

The worker would have to be pretty damn stoned, drunk, stupid, or disgruntled for this to happen, but it is possible.

Another possibility is that the coils are not tied together tightly and if the mattress was stored in an upright position some of the coils may have shifted and leaned over.

This would make these coils shorter and cause a mattress to have a dip.

Can you flip a one sided mattress?

A one-sided mattress cannot be flipped because the manufacturers realized that two-sided mattresses last longer, which means you purchase fewer mattresses in your lifetime.

This is bad for their business so they eliminated this design to increase their future revenue potential.

TIP: Rotate the mattress every month or twice per year. This changes the heaviest pressure points on the mattress where the heavier person’s torso and hips are now where the spouse’s lower, and lighter, half of his or her body was before the rotation. This may increase the life of the mattress by 25%.

TIP: Extend the life of your mattress by flipping it to the non-use side and add a four-inch foam mattress. This should be enough to make the “wrong side” comfortable and additional toppers can also increase the comfort if necessary.

Actually, this can also work for the good side and potentially extend the life an additional 10 – 20% by slightly distributing the weight over a larger area.

How to Fix a Sagging Mattress

Solutions for how to fix a sagging mattress include:

  • Installing a sheet of 3/4” plywood between the mattress and the box spring (not OSB or it will damage the mattress. Don’t be cheap and save a few bucks on the plywood and destroy your expensive mattress.

    Cut the plywood to size and if more than one sheet is required install the plywood perpendicular to the bed. This way you won’t be sleeping on the wood joint all along your body and if it is a narrow piece it won’t slip out and fall on the floor.

    Make round corners to prevent them from poking into the mattress and cause damage. Also lightly sand the edges for the same reason using 60 grit sandpaper.

    To read my article Plywood Bed Frames: Alternatives, How-To, Costs, and Tips please click here.
mattress in trash
Don’t through your mattress out yet. It can still be saved!
  • Replacing the damaged or sagging slats in the platform bed frame. Perhaps the manufacturer sells these separately or you will have to purchase 1” x 3 (or 4)” lumber (strapping) at your local hardware store.
  • Installing a four-inch foam mattress on top of your mattress to help distribute the weight.
  • Installing the mattress on the floor.

Will a mattress topper help a sagging mattress?

A mattress topper can help a sagging mattress a small amount by distributing the weight over a larger area and filling in the sagging area with the additional material. If the sagging is more substantial a four-inch foam mattress with a topper can provide better help to a sagging mattress.

Ever wonder how much a twin bed weighs on average? Check out my article here to see plus exactly how much the top models weigh.

Scott Boyd

A semi-retired workaholic in Thailand is a challenge. It is too hot to keep building adobe and earthbag buildings so a new project was needed. I became interested in bed frames after purchasing a bamboo bed frame from a local supplier here and I learned there is little information about them on the Internet. So now I spend my days researching, testing, and reporting my findings to help others while having an occasional beer and istening to 60s and 70s B side rock, blues, and much more.

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