Why bamboo nightwear feels cool without being cold
Short answer: The cool feeling comes from evaporation, not temperature. The fabric moves moisture from your skin into the air, and evaporation takes heat with it. That is why it feels cool when you are warm but not cold when you are chilly.
Evaporation cools
When moisture turns from liquid to vapour, it uses heat. That heat comes from your skin, which is why it feels cool. The fabric is not colder than other fabrics, it is just better at moving moisture to where it can evaporate. It is the same principle as a breeze feeling cool on damp skin.
Why you notice it at night
At night your body gives off moisture, even when you do not feel that you are sweating. If that moisture stays in the fabric, it turns clammy and warm. A fabric that moves it along keeps the skin drier and gives a more even feel through the night. You notice it most under a duvet, where the air stays still.
Why it does not feel cold in winter
If you are not sweating, there is no evaporation, and the fabric insulates like any other. That is why it works all year. The cool feeling only shows up when there is moisture to move. If you are cold and dry, you simply feel a soft fabric. See men's bamboo nightwear.
A smooth fabric against the skin
Bamboo viscose has a smooth surface that feels cool to the touch at first. It is the same sensation you get from silk. It is not because the fabric is colder, but because it lies close to the skin and conducts heat a little differently from a rougher weave. After a moment it feels neutral.
Fit plays a part
Nightwear that fits loosely leaves room for air between fabric and skin, which helps moisture escape. If it fits very tightly, moisture has a harder time moving on. So if you often run warm at night, choose a set with a relaxed fit, and go a size up rather than down.
What spoils the effect
Fabric softener leaves a film that stops moisture getting into the fibre. Then the whole effect disappears, and the fabric behaves like an ordinary one that holds moisture. Wash without softener, at 40 degrees, with a mild detergent. More on this in washing and care.
The same principle in bedding
Sheets and covers in the same material work in the same direction. When both nightwear and bedding can move moisture, it does not get trapped between the layers. With bamboo nightwear but bedding that holds moisture, you lose some of the effect. See bamboo bedding if you want both in the same material.
The duvet matters most
Even the best nightwear cannot make up for a duvet that is too warm for the season. The duvet holds most of the heat, so if you are hot at night, it is often the first thing to change. Nightwear and bedding can then do the rest by keeping the skin dry under the duvet.
No need to worry about getting cold
Some people worry about feeling cold in a fabric described as cool. There is no reason to. The fabric keeps you warm like other clothing when you are dry, and in winter it is the duvet and the room temperature that decide whether you are cold. A set with long sleeves and legs suits cold nights well.
Frequently asked questions
Is bamboo fabric colder than cotton?
No. It just moves moisture faster, and evaporation is what cools the skin. When your skin is dry, it feels just as warm as other fabrics do.
Why does it not work in winter?
It does. If you are not sweating, there is no evaporation, and it insulates like any other fabric. The cool feeling only comes when there is moisture.
Can the effect disappear?
Yes, if the fabric is washed with softener. The film stops moisture getting into the fibre. Wash at 40 degrees without softener and the effect is kept.
See our range of bamboo sleepwear.
