Sapphire Sleep’s 14" Cool Phase Split King Mattress is a 14-inch split king mattress with an all-foam build and a cool-touch phase-change cover. In our testing, it stood out for motion isolation and initial surface cooling while keeping most back and side sleepers in good alignment. The trade-offs were slower position changes and edge support that felt fine for sleeping but only average when sitting.
Table of Contents
Product Overview
| Mattress | Overall Score | Pros | Cons | Ideal For |
|---|---|---|---|---|
| Sapphire Sleep 14" Cool Phase Split King Mattress | 4.1/5.0 | Cool-to-touch surface, excellent motion isolation, steady support | Slow response, average edge stability when sitting | Couples and hot sleepers who like foam |
Final Verdict
If you want a quieter all-foam mattress with a cooler surface feel, this one deserves a look. Our testing showed dependable midsection support for back and side sleep, very low motion transfer, and contouring that never turned mushy. The main trade-offs are slower response and edge support that compresses more than we’d like when sitting.
Who It’s For:
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Couples sensitive to partner movement
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Back and side sleepers who want contouring with support
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Hot sleepers who like a cool first-contact feel
Who It’s Not For:
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Dedicated stomach sleepers who need a firmer, flatter surface
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People who want the quicker bounce of a hybrid mattress
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Anyone who sits on the edge a lot
How We Tested It
We rotated this mattress into our regular mattress testing protocol over several weeks. I slept on it on my back and side and tracked Support and Pressure Relief with next-morning lumbar comfort and hip alignment notes. Marcus focused on Cooling and deeper support under a heavier build, paying attention to heat buildup and any hammock effect. Jenna and Ethan repeated Motion Isolation, Edge Support, and Responsiveness checks by getting in and out of bed, changing positions near the perimeter, and sitting on the edge.
Our Testing Experience
The cool-to-the-touch cover is the first thing you notice. It feels cool on contact, then the top foams ease into a light cradle instead of a deep sink. On my back, my lower back settled in without my hips dropping. On my side, I got enough cushioning at the shoulder and hip to stay comfortable.
Marcus said it slept cooler than most all-foam beds he has tried, though he still noticed some warmth collect under his torso after staying in one spot. Jenna’s quiet-room partner test was a clear win: Ethan rolled, got up, and settled back in with very little disruption, which should appeal to couples who wake easily. The downside showed up during quick turns, when the foam feel made movement take more effort than a springier mattress.
What we liked:
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Cool first-contact feel and steadier temperature through the night
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Strong motion control for shared sleep
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Balanced contouring that kept my lower back supported
Who it is best for:
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Couples who wake easily from movement
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Back and side sleepers who want a supportive foam cradle
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Adjustable-base users who prefer foam
Where it falls short:
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Combination sleepers who want faster turns
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People who sit on the edge every morning
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Strict stomach sleepers who need a flatter, firmer surface
Pros & Cons
| Pros | Cons |
|---|---|
| Cool-to-touch surface | Slower response for quick turns |
| Excellent motion isolation | Edge sit support is only average |
| Supportive, steady foam cradle | Less bounce than many hybrids |
| Adjustable-base friendly | Foam “hug” may feel restrictive to some |
Details
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Price (Split King): $4,799.00
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Mattress height: 14"
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Size: Split King
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Cover: cool-touch phase-change fabric with a non-quilted smooth mesh cover
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Comfort layers: 1.75" breathable memory foam, 2" gel-infused memory foam, 1" comfort memory foam
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Support layers: 2" poly support foam, 8" high-density support foam
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Adjustable-base compatible: Yes
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Trial: 101-night trial for eligible direct website purchases
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Warranty: 20-year limited warranty (10 years full, 10 years prorated)
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Feel (in our tests): medium to medium-firm with slow contouring
Review Score
All scores below use a 5-point scale.
| Metric | Score | Remarks |
|---|---|---|
| Support | 4.2/5 | In our tests, hips stayed level and the lower back stayed supported in back and side positions. |
| Cooling | 4.4/5 | The cover felt cool on contact and managed heat better than most foam beds we test, though one spot could warm up over time. |
| Pressure Relief | 4.1/5 | Shoulder and hip pressure eased without an overly deep sink. |
| Motion Isolation | 4.6/5 | Partner movement stayed muted in overnight use and repeated in-and-out tests. |
| Responsiveness | 3.7/5 | Comfortable contouring, but quick turns took more effort than on hybrids. |
| Edge Support | 3.8/5 | Stable enough near the edge for sleep, but sitting compressed more than we wanted. |
| Durability | 4.0/5 | The support base felt steady, and the foams rebounded consistently during our test window. |
| Overall | 4.1/5 | A cooling-leaning foam mattress with strong motion control and balanced support, but less bounce and weaker edge sitting. |
Buying Guide
Pick this mattress if you want steady foam contouring and you mostly sleep on your back or side. If you move around a lot, a faster-responding bed may suit you better, and frequent edge sitters should look for stronger perimeter support. Shoppers who want more lift and airflow can compare it with the Brooklyn Bedding Aurora Luxe, while people who want a more traditional hotel-style feel may prefer the Saatva Classic.
Limitations
The biggest trade-off is pace. The contouring feel can make quick pivots feel slow, especially for frequent position changers. Edge sitting is also a weak point: sleeping near the perimeter felt fine in our tests, but sitting there compressed the foam more than we wanted. It is also a tougher fit for strict stomach sleepers who need a flatter surface.
Alternatives
Why choose this model:
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You want a cool-touch foam surface and a quieter night
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You are highly sensitive to partner movement
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You prefer steady contouring over springy bounce
Alternatives to consider:
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Saatva Classic: stronger edge sitting and faster turns
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Brooklyn Bedding Aurora Luxe: cooler airflow and more bounce
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TEMPUR-Adapt: deeper contouring for pressure-focused comfort
Pro Tips
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Give it a short break-in period so the surface feel becomes more predictable.
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Use a breathable mattress protector to help preserve the cool-touch feel.
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If you are heat-sensitive, pair it with lighter bedding and breathable sheets.
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On an adjustable base, a slight knee lift can make reading more comfortable.
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Keeping the bed a little flatter can make turning easier.
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Use a supportive pillow height when side sleeping to help keep your neck aligned.
FAQs
Does the mattress feel “stuck” like some memory foam beds?
Somewhat, but not severely. In our tests it felt more like a steady foam cradle than a deep sink, though quick turns still took extra effort.
How well does it work for couples?
Very well. Motion isolation was one of its best results, and Jenna stayed mostly undisturbed when Ethan got in and out or rolled over.
Is it good for hot sleepers?
Better than most all-foam models we test. The cover feels cool on contact, but Marcus still noticed some warmth build under his torso over time.
What sleep positions fit best?
Back and side sleep were the strongest matches in our tests. Strict stomach sleepers may want a firmer, flatter surface.
