Cotton is what most men sleep in: an old t-shirt, a pair of cotton pyjamas, or nothing at all under cotton sheets. It is the default because it always has been.
The sleep research gives it little support. A handful of lab studies have tested sleepwear fabrics against each other, and cotton has not come out ahead. People fell asleep faster in a fabric that handles moisture better.
Here is what those studies found, why moisture explains it, and what independent lab testing showed when we put SERIS™ against cotton.
What the sleep studies found
The main study is Chow and colleagues, published in 2019 in Nature and Science of Sleep. Thirty-six healthy adults aged 50 to 70 slept in a lab held at 30°C and 50% humidity. On separate nights they wore cotton, polyester and merino wool sleepwear, all knit the same way and matched for thickness. Sleep was measured with polysomnography, which records brain waves, eye movement and muscle activity.
Cotton fared badly:
- Falling asleep. Among the over-65s, people took 26.7 minutes to fall asleep in cotton, against 12.4 minutes in wool.
- Waking in the night. Poor sleepers spent more time awake during the night in cotton than in wool.
- Across all measures. Cotton did not beat either of the other fabrics on any of the sleep measures.
An earlier study from the same group, in 2016, tested cotton against wool in young adults in cooler rooms. At 17°C, wool shortened the time it took to fall asleep. At 22°C there was no difference.
A 2024 systematic review in the Journal of Sleep Research, by researchers from the same group, concluded that sleepwear fabric can affect sleep through skin temperature and thermal comfort.
The wool industry funded both sleep studies, and the effects were modest. The direction is consistent: across both studies, wool beat cotton on how quickly people fell asleep.
Why cotton struggles
It comes down to moisture.
As you fall asleep, your core temperature drops. Your body sheds heat through your skin, and in a warm bed you sweat. That moisture has to go somewhere.
Cotton absorbs sweat and holds it. The damp sits in the fabric against your skin, and the air between you and your sleepwear stays warm and wet. The researchers behind the 2019 study pointed to moisture handling as the likely reason cotton trailed.
A fabric for sleep needs to move moisture away from your skin and let it go. That property can be measured, so we measured it.
SERIS™ against cotton: the lab results
We sent SERIS™ to SGS, an independent testing laboratory, with a cotton jersey as the control. We tested both SERIS™ colourways, Jet Black and Glacier Grey.
Moisture management. This test puts liquid on the skin side of the fabric and tracks where it goes.
- SERIS™ moved moisture away from the skin side and through to the outer face. Its one-way transport index was +291 (Jet Black) and +321 (Glacier Grey). A positive score means the fabric pulls moisture away from the skin. A negative score means moisture collects on the skin side.
- Cotton scored −801. The moisture stayed on the skin side and never reached the outer face during the test.
- Classification. SGS classified both SERIS™ colourways as a Moisture Management Fabric. The cotton control did not qualify.
Airflow. SERIS™ Glacier Grey let through around 16% more air than cotton: 625 mm/s against 538 mm/s.
Stretch and recovery. SERIS™ stretched more than twice as far as cotton (194% against 77%) and recovered its shape better afterwards. It moves with you when you turn over.
For sleep, the moisture result matters most. It is the property the sleep research points to, and it is where SERIS™ and cotton behaved most differently.
What we claim, and where we stop
No one has run a sleep study on SERIS™ yet, including us.
Here is what we can say. The sleep research shows people sleep worse in cotton than in a fabric that handles moisture better. Independent testing shows SERIS™ handles moisture far better than cotton. We built unsuited on those two findings.
A sleep study on SERIS™ itself is the one we most want to run.
Common questions
Is cotton good for sleeping in?
It feels familiar, but the sleep research gives it weak support. In lab studies, people took longer to fall asleep in cotton than in a fabric with better moisture handling. Poor sleepers also spent more time awake. Cotton absorbs sweat and holds it against your skin.
What should I look for in sleepwear fabric?
Moisture management comes first: the fabric should move sweat away from your skin. Airflow and stretch come next. Ask for independent test results and look past the marketing adjectives.
What is SERIS™?
SERIS™ is the fabric unsuited sleepwear is made from: 93% micro modal air, an ultra fine fibre made from wood pulp, and 7% elastane. SGS classified it as a Moisture Management Fabric in independent testing. It outperformed cotton on moisture transport, airflow (tested on Glacier Grey) and stretch.
Is there proof SERIS™ helps you sleep?
Not yet, because no sleep study has tested SERIS™. The sleep research links better moisture handling to better sleep than cotton. Lab testing shows SERIS™ handles moisture far better than cotton. That is the case we make.
What about wool?
Merino wool has done well in sleep studies, and it shares the property that matters: good moisture handling. People in the 2019 study did rate it slightly pricklier than cotton or polyester. SERIS™ is a smooth, fine fibre, and it is the fabric we chose to build a brand on.