Short answer: Ask five things. What is the fibre. How was the fabric constructed. Which test, which version, and on what garment. Is there a data table or only a conclusion. And was the fabric washed before testing. A claim that survives all five is evidence. A claim that survives none is copywriting.
Every section starts with the plain version, then goes deeper for anyone who wants the detail. Read only the cream boxes and you will still get the whole picture.
Read six cooling sleepwear sites in a row and they say almost exactly the same thing. Moisture wicking. Breathable. Temperature regulating. Cool and dry all night. Some of those brands have run laboratory tests and some have not, and from the outside the sentences look identical, because words are free and testing is not.
Question 1: do they tell you what the fabric actually is?
In plain termsIf you cannot find out what the cloth is made of before you buy it, that was a decision, not an oversight.
The deeper dive
A striking number of cooling sleepwear brands never state fibre content anywhere a shopper can find it before buying. A trade name is not a fibre. An engineered cooling knit is not a fibre. If the composition only appears on the care label after the parcel arrives, someone made that choice deliberately.
Ours is polyester. Kottinu is an engineered polyester microfiber knitted at 159 g/m², first developed for firefighter base layers and medical scrubs, now made for hot sleepers and night sweats.
Question 2: is the breathability claim about the fibre or the fabric?
In plain termsNo fibre is breathable or unbreathable on its own. How the cloth is knitted decides it. Anyone claiming otherwise, in either direction, is overselling.
The deeper dive
If you search for cooling pajamas you will find advice telling you to avoid polyester because it traps heat and does not breathe. That advice fairly describes most polyester most people own: heavy, tightly knitted, coarse filaments, finished for cost.
What does not follow is the jump from that garment to the polymer. Breathability is a property of a fabric, not of a fibre. It is set by knit structure, stitch tightness, weight per square metre and filament fineness, and the same fabric type can vary several times over once those change. The full version is in what makes a fabric breathable, where every one of the twelve fibres in our scorecard is rated Varies for air flow for exactly this reason.
Question 3: which test, which version, and on what?
In plain termsWhich test, and which version of it. Standards get revised, and a result under one revision is not the same as another.
The deeper dive
There are four standards that matter in this category, and a claim worth anything will name the one it rests on.
| Standard | What it measures |
|---|---|
| AATCC 195 | Liquid moisture management, the composite rating |
| AATCC 197 | Vertical wicking, how far liquid travels |
| AATCC 201 | Drying rate |
| ASTM D737 | Air permeability, the real measure of breathability |
Our own comparison was run across all four of them, against four other wicking sleepwear brands. The brands are shown unnamed.
The four test methods and their versions are printed on the chart itself, which is more than most brands will give you.
Question 4: is there a data table, or only a conclusion?
In plain termsAsk for the rows, not the headline. A brand showing you one flattering number chose which numbers you get to see.
The deeper dive
A moisture management test produces around ten separate numbers. The rows are where you learn whether a fabric moved liquid quickly, spread it widely and released it fast, or simply scored well on a composite that rewards something else. We explain why that distinction decides your night in why moisture-wicking pajamas still leave you soaked.
Question 5: was the fabric washed before it was tested?
In plain termsBrand new fabric still has factory chemicals on it that wash out. Testing it unwashed describes a garment you will own for about a week.
The deeper dive
New fabric usually carries finishing chemistry from the mill. Those finishes can suppress wicking heavily and they wash out over a few cycles. A fabric can therefore test badly when new and well after laundering, or be tested at its single most flattering moment. Almost nobody discloses which.
The honest note on synthetics
Two things are true at once and we would rather say both.
Polyester is a plastic, and like all synthetic textiles it sheds microfibres in the wash. A wash bag made to capture them is cheap and genuinely effective, whoever made your clothes.
And: for lifting liquid sweat off skin and releasing it quickly, engineered synthetics do a job that highly absorbent natural and cellulosic fabrics structurally cannot, because a fibre that holds water is slow to give it back. That is why this fabric class exists in firefighting and medical work, and it is why it suits night sweats.
Choosing sleepwear is a trade-off, not a morality test.
Common questions
Does moisture-wicking actually mean anything?
Yes, but only when it is tied to a test. Wicking is measurable under AATCC 197 and AATCC 195. Used without a named method, the word carries no information.
Is polyester bad for pajamas?
It depends on the fabric, not the fibre. Heavy tightly knitted polyester sits hot. A light open knit of fine filaments moves liquid well and dries fast, which is why the fibre class is used in technical workwear.
How do I know if a cooling claim was actually tested?
Ask which laboratory method it rests on, and whether the brand will show you more than a single headline number. If they cannot name a method, there is probably no test behind it.
Do brands have to prove cooling claims?
Advertisers are expected to hold substantiation for objective performance claims at the time the claim runs. Whether a brand will show it to you is a different question, and worth asking.
Start with what makes a fabric breathable, then look at the NightCool collection or the men's NightCool collection.
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