This is the complete set of replacement foam side rails for a Sleep Number® FlexTop King bed — the firm foam frame that surrounds the air chambers and gives your mattress its supportive perimeter and seating edge. Over time these rails compress and soften, so the edges feel weak and you roll toward the middle. This set rebuilds the entire perimeter so your bed feels solid and supportive again, without touching the air chambers, pump, or cover you already own. Made in the USA.
FlexTop King
Complete perimeter set
2.6 lb density
85 ILD — firm edge
6" or 7" heights
Optional center rail
What you get
The complete set includes all four perimeter rails — both side rails plus the head and foot rails — sized for the FlexTop King. These are a higher density with a better seating edge than the originals: 2.6 lb density and a firm 85 ILD for stronger, longer-lasting edge support. You simply cannot go wrong rebuilding the full perimeter at this level of quality.
Should I add the center rail?
FlexTop King beds split at the head so each side articulates independently on an adjustable base. Many setups use a center rail down the middle for extra support between the two air chambers. If your bed has one now (or you want that added center support), choose Center Rail: Yes. If not, choose No for the standard four-rail set. Not sure? Call us at 610-327-2322 and we will help you confirm.
Which height should I choose?
Your rail height should match the height of your air chambers so the perimeter sits even with the chambers — most FlexTop King beds use 6" or 7" rails. Measure your current rails (or your inflated air chamber height) and match it. Not sure how to measure? 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
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Includes: all four perimeter rails (two sides, head, foot), with optional center rail
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Density: 2.6 lb — higher than the original
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Firmness: 85 ILD — firm, supportive edge
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Height options: 6" or 7"
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Made to order in the USA
Rebuilding the whole bed?
New rails restore the perimeter, but if the comfort layer over your air chambers has also worn out, replace it at the same time for a complete refresh. Choose your feel from our FlexTop King comfort foams: soft, medium (closest to original), or firm regular foam, cooler-sleeping gel memory foam, natural latex, or an egg crate topper. Browse everything in our FlexTop Split-Head collection or the full Sleep Number repair parts collection.
Frequently asked questions
What are foam side rails?
They are the firm foam frame around the air chambers that gives your mattress its supportive edge and shape. When they soften, the edges feel weak and unsupportive; replacing them rebuilds the perimeter.
Do I need the center rail?
FlexTop King beds split at the head, and many use a center rail down the middle for added support between the two chambers. Choose Center Rail: Yes if your bed has one or you want that extra support, or No for the standard four-rail set. We are glad to help you confirm — call 610-327-2322.
What height should I order?
Match your rail height to your air chamber height so the perimeter sits even with the chambers — most FlexTop King beds use 6" or 7". Measure your current rails or inflated chamber height to confirm.
Will this fit my bed?
This set is made to order for the Sleep Number FlexTop King split-head configuration. If you also need a new comfort layer or cover, see the rest of our FlexTop Split-Head collection.
