This replacement gel memory foam is our premium comfort layer for a Sleep Number® FlexTop King bed — the layer that sits on top of the air chambers and gives the surface its feel. Unlike our regular foams, this is a true gel memory foam: it contours and cradles your body, relieving pressure, while the gel and open-cell structure keep it breathable so it sleeps cooler than most memory foams. At a durable 4 lb density it is far denser than the typical 2 lb or 3 lb memory foam used in name-brand mattresses, with very little off-gassing. Replacing a worn comfort layer eliminates body impressions and sagging and restores a cool, contouring surface, without touching the air chambers, pump, or cover you already own. Made in the USA and CertiPUR-US® tested.
FlexTop King
Gel memory foam
Cooler-sleeping
4 lb density
2"–4" thickness
CertiPUR-US® tested
What size is this? FlexTop King explained
This is made for the FlexTop King. It is one solid King-size foam layer (76" × 80") with a 34" cut from the center of the head running toward the middle, which lets the two heads of the bed raise independently on a FlexFit adjustable base. Even with that head cut, the foam is a single piece with one uniform feel across the whole surface. Choose your height below.
Is your FlexTop bed built from two separate Twin XL pieces?
Some FlexTop beds use two separate Twin XL foam layers (38" × 80" each) instead of one solid piece with a head cut. If that is how yours is built, order two Twin XL layers from our standard gel memory foam instead. Two separate Twin XL pieces is also the only way to set a different feel on each side of a FlexTop bed. Not sure which you have? Browse our standard foam collection or call us at 610-327-2322.
What this foam feels like
This is a medium feel with the signature memory-foam quality: instead of sitting on top of the foam, you sink in gently and it molds to your body, cradling your shoulders and hips and easing pressure points. It is especially popular on Euro Top and smooth-top FlexTop models where that plush, contouring surface is what owners are after. The gel and open-cell structure let it breathe, so it runs cooler than the dense, heat-trapping memory foam many people have had bad experiences with. If you prefer a responsive surface that you rest on top of rather than sink into, our regular poly foams are the better fit — see the comparison below.
Gel is a “mimic” foam — and the smart two-layer build
One thing that makes gel memory foam unique is that it is what we call a mimic foam: it largely takes on the firmness of whatever sits beneath it. Put it over a soft base and the whole surface feels soft; put it over a firmer base and it feels firmer — all while keeping its cool, contouring memory-foam character on top.
If you are replacing all of your foam, a popular FlexTop King build is a 2" gel layer on top of a 2" medium regular foam base (both cut for the FlexTop King).
Why two 2" layers instead of one solid 4"
Because gel mimics the layer below it, this build is a smart long-term investment. If you ever want to change the overall feel of the bed, you only swap the inexpensive 2" base layer — a soft base for a plusher bed or a firm base for a firmer one — and the gel on top takes on that new feel. With a single solid 4" block, changing the feel later means rebuying a full 4" of foam instead of just a 2" layer.
Want a different feel on each side of the bed? On a solid FlexTop King foam that is not possible — it is one uniform piece. That only works if your bed is built from two separate Twin XL halves; in that case, build each side from our standard Twin XL gel and regular foams instead.
Gel memory foam or regular foam?
It comes down to the feel you want:
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Choose this gel memory foam if you want a contouring, pressure-relieving, cooler-sleeping surface that hugs your body — the premium, plush option.
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Choose a regular foam if you want to rest on top of a more responsive surface. Our medium regular foam is the closest match to Sleep Number original foam; soft and firm options are also available.
Which thickness should I choose?
The thickness you pick sets how much foam sits over the air chambers, and it also affects your shell height. Most beds use a 2" or 3" comfort layer. Match the thickness you have now to keep the same shell height, or go thicker for a deeper, more enveloping memory-foam feel (which raises your shell height by the difference, so order a cover to match if you are replacing that too).
Not sure how thickness ties into shell height? Our guide to measuring your Sleep Number bed walks through it, or call us at 610-327-2322.
Specifications
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Fits: Sleep Number FlexTop King (solid King foam with 34" center head cut)
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Type: gel memory foam — contouring, cooler-sleeping
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Feel: medium, with memory-foam cradle (mimics the layer beneath it)
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Density: 4 lb — far more durable than typical 2–3 lb memory foam
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Thickness options: 2", 3", or 4"
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Low off-gassing, CertiPUR-US® tested, made to order in the USA
Compare our FlexTop King foams
All of these are cut for the FlexTop King. Here is how the feels compare so you can pick the right one:
| Foam |
Feel |
Firmness |
Best for |
| Soft Regular |
Plush, sink-in |
12 ILD |
Softening a bed that feels too firm |
| Medium Regular |
Balanced, original feel |
35 ILD |
Most people; firming up a sagging bed (closest to original) |
| Firm Regular |
Extra-firm, little give |
50 ILD |
Sleepers who want a very hard surface |
|
Gel Memory (this page) |
Contouring, cooler, sink-in |
Medium (cradle) |
Pressure relief; plush premium feel |
| Latex |
Buoyant, responsive, on-top |
29 ILD (medium) |
Lively support; durable upgrade (not a Sleep Number foam) |
| Egg Crate |
Light cushion + airflow |
35 ILD |
Economical comfort and cooling boost |
Will this fit my bed?
This is made to order for the FlexTop King split-head configuration. If your bed's foam side rails have also softened, you can rebuild the firm edge at the same time with the FlexTop complete rail set. Browse everything for your bed in our FlexTop Split-Head collection, or see the full Sleep Number repair parts collection.
Frequently asked questions
Does memory foam sleep hot?
Many do, but this one is built to run cooler. The gel and open-cell structure make it more breathable than typical dense memory foam, so it dissipates heat better while still giving you that contouring feel.
What is a “mimic” foam, and should I do the two-layer build?
Gel memory foam largely takes on the firmness of whatever is underneath it, so we call it a mimic foam. If you are replacing all your foam, a popular setup is 2" of this gel on top of a 2" medium regular foam base. The advantage is flexibility later: to change the overall feel you only swap the 2" base layer (soft for plusher, firm for firmer) instead of rebuying a full 4" block.
Can I have a different feel on each side?
Not with the solid FlexTop King foam — it is one uniform piece. A different feel per side is only possible if your bed uses two separate Twin XL halves. In that case, build each side from our standard Twin XL gel and regular foams.
Why 4 lb density?
Density is a measure of durability for memory foam. At 4 lb this is far denser than the 2 lb or 3 lb memory foam used in many name-brand mattresses, so it holds its feel and lasts longer, with very little off-gassing.
What thickness should I order?
Match the thickness of your current comfort foam to keep the same shell height; most beds use 2" or 3". Going thicker adds a deeper memory-foam feel but raises your shell height by the difference, which matters if you are also replacing the cover.
What if the foam is too firm or too soft?
No problem — we offer a 30-day comfort exchange. Return it for a full refund or credit, or keep it and take a one-time 50% off a replacement (most people choose this — nothing to ship back). See our Foam Comfort Exchange & Return Policy for full details.
