Long cotton underpants or bamboo
Short answer: As a base layer under trousers, moisture transport decides whether you get cold. Cotton soaks up moisture and gets wet, while bamboo viscose moves it on. That is why a thin layer of bamboo often feels warmer in practice than a thicker layer of cotton.
The job of a base layer
The inner layer should keep the skin dry, not be thick. Warmth comes from the air held between layers, and that only works when the skin is dry. A damp inner layer draws heat from the body, whatever you wear on top. See the styles in bamboo long johns if you want to try a thin layer.
Cotton turns cold
If you have sweated on the way somewhere, a wet cotton layer turns cold once you stand still. Many know this from cycling to work in winter or a walk in the woods, where you warm up going uphill and feel cold afterwards. Cotton holds the moisture, and then it cools against the skin.
Wool as an alternative
Wool also keeps you warm when damp and is an obvious choice for serious cold. On the other hand, many find it itchy, especially directly against the skin on the legs. Bamboo viscose is smooth and soft and can be worn alone or under a wool layer. Read more about the difference in bamboo compared with wool.
Thickness
A thin inner layer warms more than thick outer trousers alone, because it traps air close to the body. A thick base layer, by contrast, can make your trousers tight and make you sweat more. So choose a thin, close fitting layer that adds no bulk under jeans or work trousers.
Who it suits
Outdoor work, cycling and standing still in the cold are the typical situations where long underpants make a difference. The same goes for football matches, gardening and long walks in the colder months. If you are often outside for hours, the inner layer matters most. See more tips in bamboo clothing for cold days.
Washing
Bamboo viscose stays at 40 degrees and out of the tumble dryer, which can shrink the fabric and slacken the elastic. Skip fabric softener, which makes the fabric worse at moving moisture. Hang them to dry, and they keep their shape longer. All the practical rules are in the washing guide.
Fit
Long underpants should sit close all the way down without pressing at the waistband or ankles. If they are loose, the fabric bunches at the knees and feels uncomfortable under trousers. Bamboo viscose gives, so most people can keep their usual size. Check that they fit under your trousers without pulling.
See the range
The whole group, with long underpants, underpants and undershirts, is in bamboo underwear for men. It can help to wear the same material on both upper and lower body, so the whole inner layer works the same way. Start with the long underpants if it is your legs that get cold.
How many pairs
If you wear a base layer daily in winter, you need at least three pairs. That lets you wash without running short, and each pair has time to dry fully. If you only wear them for weekend outings, one or two pairs may be enough. See the styles in bamboo underwear for men.
When cotton is fine
Cotton long underpants work fine if you mostly stand still and do not sweat, for example on a short outing or indoors in a cold house. The problem starts when you warm up and then cool down again. Then moisture makes the difference, not thickness. Choose by how much you move.
Frequently asked questions
What is best as a base layer?
A layer that moves moisture away from the skin rather than soaking it up. Bamboo viscose does this better than cotton and therefore feels warmer when you switch between moving and resting.
Is wool better than bamboo?
Wool warms when wet and suits serious cold, but many find it itchy. Bamboo viscose is softer and can be worn alone or under a wool layer if you want both.
How thick should long underpants be?
A thin, close fitting layer is best, because it keeps the skin dry and traps air near the body. A thick layer can make trousers tight and make you sweat more.
You can find the full range at Bamboo-Clothing.com.
