Friction between two layers of clothing
Short answer: When two layers slide against each other, they wear on each other instead of on the skin. That is one reason a smooth inner layer feels comfortable.
The movement has to happen somewhere
The body moves all the time. Either the fabric slides against the skin, or two layers slide against each other. The latter is far preferable, since skin is much more sensitive than fabric. The aim is not to remove movement but to move it to where it does least harm.
Smooth on smooth glides best
Two smooth fabrics slide easily, and friction stays low. That is why a smooth base layer under a rough sweater removes discomfort. The sweater moves freely over the layer, and the layer stays against the skin. See bamboo leggings for women.
The price is wear on the fabric
What does not wear on the skin wears on the clothing. That is why an inner layer becomes thinner over time, even if it does not look worn. It is a fair price, since fabric can be replaced while skin has to keep working. See bamboo training pants for women and bamboo training clothes for women.
Layers must not sit too tight
If two layers sit too tightly together, they cannot slide against each other, and the movement is pressed back into the skin. Give the outer layer a little room to move. That way you benefit from the inner layer without clothing feeling tight or restricting you.
Seams and folds in the layers
Where two layers lie on top of each other, a seam in one can be felt through the other. Folds in the innermost layer can press against the skin as you move. Choose layers that lie flat without thick seams, and smooth them out before you put them on.
Especially during activity
When walking, running and cycling, the movement repeats thousands of times. Even slight friction adds up to a lot of wear over a whole outing. A smooth inner layer therefore makes the biggest difference on long days when layers move a lot against each other.
Moisture changes the glide
If the skin or the fabric is wet, the glide changes. Wet fabric clings more easily, and two wet layers can stick to each other instead of sliding. That is why it helps to change into dry clothes when wet, and to choose inner layers that dry reasonably fast.
Washing protects the layers
An inner layer that is washed often keeps its smoothness better if you follow the care label. Skip fabric softener if the label advises against it, and let the clothes dry before you put them away. That keeps the surface even and friction low for longer.
Choose by the day
On a quiet day one soft layer may be enough. On a long, active day, two layers with a smooth inner layer are often more comfortable. Think about how much and how long you will move before you choose. That way you avoid changing clothes along the way.
Frequently asked questions
Why does a wool sweater chafe directly on the skin
Because wool fibers have scales that catch on the skin and move with it. A smooth layer in between often makes it more comfortable.
Are two layers always better
For activity, yes. At rest a single soft layer may be enough, and two layers can feel too warm.
Which layer should be the smoothest
The innermost, because it touches the skin. The outer one can be rougher, as long as the inner layer slides easily against it.
You can find the full range at Bamboo-Clothing.com.
