THE SCIENCE OF SLEEPING COOL
Why you sleep hot — and what actually fixes it.
Most people who sleep badly don’t have a sleep problem. They have a heat problem. Here is what your body is trying to do every night, why ordinary bedding gets in its way, and how Napfull is built to get out of it.
01 · THE BODY
To fall asleep, your body has to lose heat.
Every evening your core temperature begins to fall, and sleep pushes it lower still. It keeps dropping until the early morning hours, then climbs again before you wake.
To get there, your body opens the blood vessels in your hands, feet and face and releases heat through your skin. In a landmark study published in Nature, how widely those vessels in the hands and feet opened was the best physiological predictor of how quickly people fell asleep.
Anything that stops that heat from leaving is working against your sleep.
Sources: Kräuchi et al., Nature (1999); Okamoto-Mizuno & Mizuno, Journal of Physiological Anthropology (2012).
02 · THE BED
The climate under your covers decides how you sleep.
Sleep researchers have a name for the thin layer of air between your skin and your bedding: the bed climate. When sleep is normal, it sits at around 32–34°C and 40–60% relative humidity.
Push it warmer and the research finds more time awake, less deep sleep and less REM. Make it humid as well, and all three get worse. That is the 3 AM wake-up, measured in a lab.
Your thermostat only reaches this layer from the outside. What lies on top of you — and under your head — decides what happens inside it.
Source: Okamoto-Mizuno & Mizuno, Journal of Physiological Anthropology (2012).
03 · TWO PROBLEMS
Your head and your body overheat for different reasons.
Your face is one of the places your body releases heat — and for eight hours a night, it is pressed into a pillow. Foam and down absorb that warmth and hold on to it. That is why the cool side of the pillow never lasts.
Your body has the opposite problem. It isn’t pressed into anything; it is covered. A blanket built for warmth traps the heat rising off your skin and keeps it in the bed climate.
One problem is contact. The other is coverage. That is why Napfull makes two products — and why people who fix one usually start noticing the other.
04 · THE MECHANISM
Ordinary bedding holds heat. Napfull lets it leave.
Every Napfull product is built around one idea: heat needs somewhere to go. Three things make that happen.
Conduct
Cool-to-the-touch fibers draw heat away from your skin the moment you make contact.
Breathe
An open structure lets warm air escape instead of pooling around you.
Wick
Moisture moves out of the bed climate, so the air around you stays dry instead of clammy.
05 · THE MEASUREMENT
Cool you can measure: Qmax 0.40–0.45.
Qmax is the standard lab measurement for how cool a fabric feels to the touch. It records how much heat flows from warm skin into the fabric in the first instant of contact, in watts per square centimeter.
The Chinese national standard for cool-feeling textiles, GB/T 35263-2017, draws its line at 0.15 W/cm². Napfull’s fabric measures 0.40–0.45 — between 2.7 and 3 times that line.
One honest note: Qmax captures the first moment of contact, not the whole night. Staying cool until morning is the job of breathability and moisture control. That is why Napfull is engineered for all three.
Napfull value: lab test report from our manufacturer ([LAB NAME, YEAR]). Threshold: GB/T 35263-2017, Textiles — Testing and evaluation for cool feeling in contact instant.
06 · THE FABRIC
Why some fabrics feel cool and others don’t.
Heat moves from your skin into whatever it touches. The more fiber is actually in contact with your skin — and the better that fiber conducts heat — the faster warmth is drawn away.
Loose, fluffy fibers touch you at only a few points and trap still air between them. Still air is an insulator. It is exactly what makes a down comforter warm, and exactly what you don’t want at 3 AM.
Napfull’s fabric is built for contact. That is what a 0.40+ Qmax is measuring.
Material composition — Napfull Core™: [FILL IN] · Napfull Air™ cover: [FILL IN]
07 · SAFETY
Tested for harmful substances. Down to the thread.
You spend a third of your life in bed, with your face against your pillow. So Napfull is certified to OEKO-TEX® STANDARD 100 — an independent certification in which every component, from fabric to thread, is tested against a list of harmful substances.
You don’t have to take our word for it. Every certificate has a number you can check yourself.
Verify any OEKO-TEX® certificate at oeko-tex.com.
OEKO-TEX® STANDARD 100
Every component tested for harmful substances
Certificate no. [CERT NO.]
08 · CARE
Keep it cool for years.
Cooling fabric works through direct contact with your skin. Keep the fibers clean and uncoated, and it keeps working.
Wash cold
30°C (85°F) on a gentle cycle, with a mild detergent.
Skip the softener
Fabric softener leaves a coating on the fibers that stops moisture from moving out.
Dry low or hang
Tumble dry on low, or hang to dry. The fabric releases water fast.
THE FIX
Now you know why. Here’s the fix.
Start where the heat wakes you. Throwing the covers off? Start with the blanket. Flipping the pillow? Start with the pillow. Most people end up with both.
Every Napfull product comes with a 100-night trial and free returns.
References: Kräuchi K, Cajochen C, Werth E, Wirz-Justice A. Warm feet promote the rapid onset of sleep. Nature (1999). · Okamoto-Mizuno K, Mizuno K. Effects of thermal environment on sleep and circadian rhythm. Journal of Physiological Anthropology (2012). · GB/T 35263-2017, Textiles — Testing and evaluation for cool feeling in contact instant.