Wicking magic of Wool
Rather than straining perspiration moisture and vapour through the tiny, tiny gaps in a non-absorbent synthetic knit, wool’s inner core (cortex) absorbs moisture—between 27% and 36% of its weight.
This absorbed moisture is then impacted by the lower humidity, air movement and (potentially) sunlight on the outside of the garment. The result: evaporation.
With so much moisture being absorbed, will a wool garment feel soggy? If it becomes saturated and is confined to a damp or high-humidity environment, it could. (Synthetics are often a better choice for excursions where persistent rain is likely.)
Yet wool has the capacity to both absorb moisture (in a vaporous state such as perspiration) while also resisting water (in a liquid state such as light rain). This is one of the almost-too-good-to-be-true marvels of wool.
Wool fibres have a scaly exterior layer called the cuticle, and that is overlaid with the epicuticle, itself coated with lanolin, a waxy, water-shedding film. It is the epicuticle and its waxy coating that makes wool resistant to mist and light rain (hydrophobic). It is this hydrophobic layer that touches your skin, minimizing (or eliminating) any sensation of dampness.
A very sweaty person can overwhelm any fabric. During those moments a wool garment will likely feel less damp and clammy on your skin than a synthetic garment, but it may feel weightier. A synthetic garment will dry out and feel lighter more quickly.
As a total sweat machine myself, I have to laugh at enthusiastic promotional claims (“Keeps you dry!”) sometimes linked to wicking garments. If a T-shirt shut down my ability to sweat, I’d be worried. What wicking fabrics do is allow you to feel drier faster than if you were wearing cotton or some other nontechnical fabric—and that’s a huge positive that, in my mind, makes them worth the money.
Wool Texture and Temperature Regulation
Some people may be hesitant to consider wearing wool as a next-to-skin fabric.
Realize that performance underwear designed with wool uses merino wool, which consists of “ultrafine” fibres just 17.5 microns in width, fine enough that people will not experience the scratchy sensation often associated with traditional wool. The average human hair, just for comparison, measures 60 microns.
A property unique to wool is its ability to release small amounts of heat as it absorbs water. This effect is known by the arcane term “heat of sorption.” Energy, in the form of small amounts of heat, is produced through the work of moisture-absorption by wool fibres. Thus, in damp conditions, a wearer could potentially collect a small amount of comfort from this phenomenon. This is in addition to the countless warmth-trapping air pockets created by all the crimps inherent merino wool fibres.
Could that make wool too warm in hot conditions? Not necessarily. Evaporating moisture within the cortex can cool the air between the wool fabric and your skin, promoting a stable body temperature. Also, breathable wool fibres can buffer skin from air heated by the sun the same way they can trap warmed air and keep it close to skin in cool conditions.
Admittedly, these nuances can be tough to detect in the field, and when conditions turn seriously cold, you will obviously need more than a lightweight wool tee to maintain a comfortable body temperature.