iMerino
Breathability
Breathability
When someone says a garment “breathes” they are referring to its ability to dissipate perspiration so that they don’t feel “clammy”. The scientific term for “breathability” is moisture buffering.
Moisture buffering
Moisture buffering refers to a textile’s capacity to absorb moisture vapour from the micro-climate above the skin when there is a rise in humidity and release it again if the humidity should drop. A textile’s propensity to absorb moisture vapour is known as its hygroscopicity, while the weight of water able to be absorbed by a fibre as a percentage of its dry weight is known as the regain.
Merino has highest regain
For synthetics the regain can be as low as 1%, for cotton it’s 24%, while merino has the highest regain with an ability to absorb 35% of its own dry weight in water. (Fig 1)
Merino has the greatest capacity to absorb moisture vapour of all apparel fibres because its internal structure is more complex than synthetic fibres, creating more sites where moisture can bind. This higher regain means that merino is better able to absorb the moisture vapour produced by the wearer and so lower the humidity in the micro-climate between the skin and the garment. (Fig 2)
Moisture transport
Further enhancing merino’s perception of breathability is its superior moisture transport. When a person is sweating the air near the skin is humid while that further away is drier. Just as different textiles have varying abilities to absorb moisture vapour as they move towards sweating skin, so do they vary in their capacity to release it again when they move away into the drier air.
Merino’s superior moisture transport
Tests conducted by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia showed that merino was twice as effective at absorbing and releasing sweat as an equivalent polyester fabric.
It is this ability to not just absorb more moisture vapour but also release it that explains why merino is so effective at reducing the uncomfortable sensation of clamminess.
Temperature drop with vaporisation
There is a further factor that enhances the qualitative assessment that merino feels more “breathable”. When a textile absorbs liquid sweat within its internal structure and it evaporates at the surface there is an accompanying drop in temperature. For most textiles, this effect is negligible because of their limited capacity to absorb moisture. But, because merino can absorb so much liquid, the temperature drop is noticeable.
Heat of sorption
Conversely, if the ambient temperature should drop, moisture from the air can be absorbed by merino and converted to bound liquid, a process that produces a rise in temperature known as the “heat of sorption”.
Thermo-neutral
This ability of merino to respond to changes in the microclimate above the skin, producing a drop in temperature when you sweat, and a rise in temperature when you chill enhances the qualitative sensation to the wearer that Australian Merino has excellent “breathability”.
Laboratory proof of merino’s breathability
A number of tests have been done which support the anecdotal evidence concerning merino’s “breathability”.
The Hohenstein Institute in Germany performed trials to investigate wearer comfort when sweaters made from different textiles were worn under rainproof outerwear, a common combination for sport and outdoor enthusiasts.
Merino superior to cotton and acrylics
The Hohenstein tests confirmed that a merino sweater absorbed more moisture vapour than cotton or acrylic equivalents and, in wearer trials, both objective and subjective assessments rated merino as providing superior comfort to either cotton or synthetics. (Fig 3)
Less clammy
In other testing, the CSIRO examined skin contact garments such as athletic shirts during vigorousexercise. The tests showed that the merino T shirt absorbed more perspiration than polyester and that wearers found merino to be far less clammy than the synthetic. (Fig 4)
Merino also came out on top in the Overall Comfort rankings (Fig 5)
Summary
The Hohenstein tests confirmed the widely held belief that merino “breathes” and is an excellent choice to wear under waterproof clothing in cold conditions, while the CSIRO testing shows that merino’s amazing ability to absorb moisture has wider application in summer sporting attire than perhaps was previously appreciated.
Sources
- CSIRO, “Wool for Comfort: Benefits of moisture absorbency in wool knitwear”
- CSIRO, “Moisture buffering”
- CSIRO, “Wool for active sports: Comfort and Performance Advantages”
All figures and tables courtesy of CSIRO unless otherwise stated.
