The base layer is the first item of clothing that should be considered for comfort and function. The comfort is to ensure that the clothing does not irritate the skin for a long period of time. The function is to move moisture away from the body and ensure that humidity does not irritate the skin as well. It is recommended that any material that absorbs water and moisture be avoided as a base layer.
The base layer should be breathable and should not be too thick or restricting. The base layer’s main job is not to insulate heat at the expense of comfort or manoeuvrability. Thermal base layers are useful for cold weather but have negative effects which can cause the body to overheat in warm weather. It is better to have mid layers deal with the job of insulating heat as they can be removed where the weather is warm or the body is too hot.
So why should you not wear cotton? Cotton is very comfortable and hypoallergenic, however it maintains moisture too easily and will lead to maintaining the sweat of the body after the body has exerted itself. As the body cools down, the sweat on the clothing will continue to try and cool the body as if it were still exerting itself and cause discomfort. Cotton is recommended for comfort and heat insulation, however is not recommended where exercise is involved.
What materials are more suitable for a base layer? Most synthetic fabrics (including hybrids) are excellent at evaporating moisture off the body during high exertion activities which is mainly due to quick drying properties. This makes synthetic fabrics most common for sports wear and modern fashion accessories. A great alternative to synthetics is wool, which is effective over a range of temperatures but can sometimes be uncomfortable even with treatment. Merino wool is one of the many alternatives which is very comfortable with both insulating properties and the ability to resist body odours.