The split top king is the best mattress format most people have never heard of — one king bed, two independently rising heads, no seam under your hips. This is the complete owner's manual: what it is, every name it hides under, which base it needs, and the sheet situation nobody warns you about.
A split top king (= flex top king = split head king) is a 76" × 80" king mattress split only through the top ~34 inches, made for adjustable bases where each sleeper raises their head independently. It needs a dual-head adjustable base and special head-split fitted sheets — standard king sheets won't stay on, and Twin XL sheets don't fit at all.
One mattress that bends at the top.
Standard king footprint — 76 wide, 80 long — with a factory split running from the head down through roughly the top third. On a compatible adjustable base, your side sits up for reading while your partner's stays flat, and from the waist down the mattress remains one seamless piece. That last part is the whole sales pitch: a split king gives more adjustability but puts a gap down the center of the marriage; the split top king doesn't.
Brands can't agree what to call it: Sleep Number says FlexTop®, others say split head king, top split king, or half split king. Same bed. If a listing describes a king that “splits at the head only,” everything on this page applies — the full naming decoder is in Flex Top vs Split Top King.
The base does the bending.
A split top mattress needs an adjustable base with two independent head sections — usually sold as “split head” or “flex top” bases. A standard one-piece adjustable base defeats the purpose (both heads rise together), and a fully split base is overkill unless the feet also split. Check three things before buying: head-section independence, weight rating per side (motors care), and whether the retailer matches the mattress split depth (~34") to the base's head-section length. Mismatched split depths are the #1 cause of the “tenting” people blame on sheets.
| Format | Mattress | Adjusts | Sheets needed |
|---|---|---|---|
| King | One piece, 76×80 | Whole bed together | Standard king set |
| Split Top King | One piece, head-split ~34" | Heads independently | Head-split fitted + king flat |
| Split King | Two Twin XLs (38×80 ×2) | Head + feet, per side | Two Twin XL fitteds + king flat |
| Twin XL (one) | One piece, 38×80 | Whole mattress, on its own base | Twin XL fitted + Twin XL flat |
| Split Top Cal King | One piece 72×84, head-split | Heads independently | Head-split Cal King fitted + Cal King flat |
The Twin XL confusion is worth clearing up here, because it is where most of the wrong sheets get bought. A Twin XL is a single mattress, 38 by 80 inches. Put two of them side by side and you have exactly the 76 by 80 footprint of a king — that pairing is what the industry calls a split king, and because they are two separate mattresses each one can carry its own firmness, its own memory foam or hybrid build, and its own head and foot movement. A split top king is not that. It is one mattress with one firmness, cut at the head only, so there is no seam under the body and no bed frame gap to bridge. For a couple the choice comes down to one question: two people who need genuinely different support should look at two Twin XLs on a split base, and two people who want one continuous surface with independent heads should choose the split top king. Neither option is better in the abstract, and the bedding is not interchangeable in either direction — a Twin XL fitted sheet has nothing to grip on a one-piece mattress, and a head-split king fitted sheet flaps loose over two separate ones.
The sheet problem, solved properly.
A standard king fitted sheet can't follow the head split — raise one side and it strains, tents, and pops a corner at 2 a.m. What you need is a fitted sheet with a matching sewn-in split and separately pocketed corners for each half of the head. The flat sheet and pillowcases stay standard king; only the fitted sheet is special. And once the right set is in the house, the five-piece bed has its own four-minute method: how to make a split top king bed.
Our Split Top King set is cut exactly for this: 100% rayon (viscose) from bamboo in a cooling sateen, 17" deep pockets, and corner straps on every corner including the two middle pieces at the split — the spot where cheaper split-top sheets give up. Bamboo matters more than usual on adjustable beds: people who sit up reading run warmer, and the fiber breathes instead of trapping that heat (the mechanism).
Split Top King · 100% Bamboo Luxe
Head-split fitted + king flat · straps on all corners incl. the split · OEKO-TEX · fits FlexTop® & split head beds.
