Slumber Cloud UltraCool Pillow

Cooling Performance in Hot Sleep

The UltraCool Pillow's headline feature is Outlast — a phase-change material originally developed for NASA spacesuits to keep astronauts thermally stable during EVAs. Outlast works by absorbing excess body heat when you get warm, storing it in microcapsules embedded in the fabric, and releasing it back to you when you cool down. Slumber Cloud claims the technology reduces heat buildup by up to 50 percent versus a standard polyester pillow.

CNN Underscored's tester, after sleeping on the UltraCool for multiple nights as part of a head-to-head with several other cooling pillows, said the UltraCool was one of only two pillows that actually cooled them off as they slept: 'It stays consistently cool without needing to flip it over, and I didn't wake up sweaty or overheated.' Good Housekeeping named it Best Cooling Pillow on the strength of the same all-night temperature regulation. Sleepopolis reviewer Logan Block, testing the Slumber Cloud Nacreous PCM cover that uses the identical Outlast tech, called it 'quite breathable' and credited it with limiting heat retention through the night.

The key distinction between Outlast and a passive cooling material like cotton or bamboo is that Outlast is bidirectional — it stores heat when you're warm AND releases it back when you cool down. That matters in the middle-of-night temperature swing window when your body temperature naturally drops and most cooling pillows then feel cold and uncomfortable. The UltraCool buffers in both directions, which is why owners describe the pillow as 'feeling neutral' rather than 'feeling cold' through a full sleep cycle. Slumber Cloud has been refining the same Outlast cover formulation across their bedding product line for years, so the manufacturing maturity is unusually high for a still-niche thermal-regulation product.

Feel and Hand

Despite the cooling-tech focus, the UltraCool is a soft, plush, down-alternative-feeling pillow. The fill is 100 percent polyester fiberfill, which gives it the lightweight moldability of a traditional fluff pillow rather than the dense, conforming feel of memory foam. The Adjustable model lets you remove fill via zipper to dial in firmness; the standard model is offered in Soft/Medium and Medium/Firm versions and ships at a fixed loft.

Reviewers consistently describe the cover as cool-on-contact without feeling slick or plastic-y. The polyester knit is engineered to drape rather than crinkle, so the pillow looks and feels like premium hotel bedding rather than a sport-cooling product. One CNN tester noted the cover material is 'durable and smooth' — a nice contrast to some PCM-coated fabrics that develop a tacky hand after a few wash cycles.

The Adjustable UltraCool uses a two-insert system — one fiberfill, one memory-foam — that lets you change the firmness profile more dramatically than a typical pillow lets you. Pulling the memory-foam insert leaves you with a soft, all-fluff pillow that feels like premium down. Leaving both inserts in produces a denser, more supportive feel that holds shape better through a side-sleeping night. Most reviewers settle on a configuration within the first week of ownership and then leave it alone.

Construction and Materials

The cover is 100 percent polyester knit with the Outlast coating applied to the fabric fibers themselves rather than laminated on as a separate layer. That distinction matters for longevity — a coating wears off; an embedded treatment lasts the life of the fabric. The fill is also 100 percent polyester, down-alternative grade, which makes the whole pillow hypoallergenic and machine-washable on cold gentle.

OEKO-TEX STANDARD 100 certification (number 05.0.9235) means the pillow is tested free of more than 1,000 harmful substances, which matters more than usual for a pillow your face touches eight hours a night. Slumber Cloud manufactures in China but provides full supply-chain transparency on the certification page. The brand has been in the cooling-bedding category for over a decade and survived multiple competitor entries, which is a useful indicator of product durability and customer satisfaction over time. Their warranty replacement track record is well-regarded across Trustpilot and dedicated bedding-review communities, even though the formal trial window is short.

Loft and Sizing

The UltraCool comes in three sizes — Standard 20x26, King 20x36, and a 48-inch Body Pillow — and two firmness options. Most reviewers recommend Soft/Medium for back and stomach sleepers, Medium/Firm for side sleepers needing more neck support. The Adjustable UltraCool lets you remove fill yourself, which is the option to pick if you sleep in multiple positions across the night.

The fill comes pre-measured in two removable inserts: a fiberfill section and a memory-foam section in the Adjustable model. Pulling out one insert dramatically changes the firmness profile, which gives you more dynamic-range control than a typical adjustable pillow that just lets you scoop out fill by the handful.

Care and Durability

The full pillow — cover and fill — is machine-washable on cold gentle and tumble-dryable on low. That's rare for a cooling pillow at this price; most PCM or gel pillows have either a cover-only wash spec or require fluffing in a dryer for 30+ minutes to recover loft. The UltraCool's polyester construction also means it dries faster than a comparable down or latex pillow.

Outlast PCM is rated for the life of the fabric — the microcapsules don't wear out under normal use because they don't physically wear; they cycle thermally. Reviewers who've owned the UltraCool for 2+ years report cooling performance is largely unchanged, which is the failure mode you'd most fear with any phase-change product.

Where It Falls Short

The 30-night trial is the shortest in this lineup by a wide margin — Saatva offers 365 nights, Coop 100, Cozy Earth 100. Slumber Cloud knows their PCM tech is good enough that most buyers commit within the first week, but if you're cautious about an investment pillow, a longer trial would be reassuring.

The cooling does work best when the pillow is closest to your skin. CNN's tester noted the cooling effect 'works best without a pillowcase,' and several reviewers on Trustpilot reported that a thick cotton percale case noticeably blunts the effect. If you can't sleep without a case, a thinner Tencel or bamboo viscose case is a better pairing than a 400-thread-count cotton.

Who It's Best For

Pick the UltraCool if you want the most-proven cooling tech in the category and don't need adjustability. Menopausal sleepers, hot-flash sufferers, summer-overheat hot sleepers, and anyone who's tried gel-infused memory foam pillows and found the cooling fades too fast will see the biggest improvement from switching to Outlast.

Skip it if you need a long sleep trial — Saatva's 365 nights is the better fit there — or if you sleep in a humid climate where a polyester fiberfill might feel less breathable than a latex or silk fill. The Cozy Earth Silk Pillow handles humidity better; the Saatva Latex Pillow handles whole-pillow airflow better.

How It Compares to Alternatives

Versus the Coop Cool+, the UltraCool gives up adjustable loft but the Outlast PCM is more proven for sustained overnight temperature regulation. Versus the Saatva Latex Pillow, the UltraCool is the cooler-on-contact option, but Saatva's pin-hole latex core breathes better through the whole pillow body in a hot bedroom.

Versus the Purple Harmony, the two pillows perform roughly equivalently on temperature, but the Purple's Hex polymer grid offers more responsive bounce-back support while the UltraCool offers a softer, more pillow-like cradle. Versus the Cozy Earth Silk Pillow, the UltraCool is the better choice for buyers who actively want a cool surface; Cozy Earth is the better choice for buyers who just want a pillow that doesn't trap heat.