This replacement comfort foam layer is the firmest foam we offer for a Sleep Number® FlexTop King bed — the layer that sits on top of the air chambers and gives the surface its feel. It delivers an extremely firm, rigid surface with little to no give. Replacing a worn comfort layer eliminates body impressions and sagging, without touching the air chambers, pump, or cover you already own. Made in the USA and CertiPUR-US® tested.
FlexTop King
Extra-firm feel
1.8 lb density
50 ILD firmness
1"–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 firm regular 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.
Trying to fix a sagging bed? Most people want our medium foam, not this one. If your goal is to firm up a bed that has gone soft, our
medium regular foam is the right call about nine times out of ten — and because you have a Sleep Number bed, you can dial the air chambers firmer on top of that. This firm foam is for the rare sleeper who truly wants an extremely hard, almost board-like surface.
What this foam feels like
This is by far the firmest option in our foam line — an extremely firm, rigid feel with little to no give, close to lying on a board. It does not cushion or contour; it is built purely for maximum, unyielding support. This is an outlier choice for sleepers who specifically want a rock-hard surface, not a general fix for a soft or sagging bed.
If you are here because your bed sags and you know you need something firmer, the medium regular foam is almost certainly the one you want. It restores firm, even support and matches the original Sleep Number feel, and you can then adjust your air chambers firmer for extra support. Customers who choose this firm foam to fix a sagging bed most often find it far too hard.
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 (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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Feel: extremely firm — the firmest of our foam options, with little to no give
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Density: 1.8 lb
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Firmness: 50 ILD
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Thickness options: 1", 2", 3", or 4"
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Quality: 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 (this page) |
Extra-firm, little give |
50 ILD |
Sleepers who want a very hard surface |
| Gel Memory |
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
How firm is this foam?
It is by far the firmest option we offer — an extremely firm, rigid feel at 1.8 lb density and 50 ILD, with little to no give, close to lying on a board. It is firmer than our medium foam and firmer than Sleep Number original regular foam.
I just want to fix a sagging bed — should I get firm or medium?
For almost everyone fixing a soft or sagging bed, the medium regular foam is the right choice: it restores firm, even support, matches the original Sleep Number feel, and you can adjust your air chambers firmer for more support on top of it. This firm foam is an extremely hard, board-like surface meant only for sleepers who specifically want a rock-hard bed.
Is this one solid piece or two?
It is one solid King-size piece with a 34" cut at the center of the head so the two heads raise independently, giving one uniform feel. If your bed instead uses two separate Twin XL pieces, order two Twin XL layers from our standard firm foam page.
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 firm layer 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.
