Waterproof breathable fabrics have come a long way in the past decade and, when coupled with design features like venting and a good fit, the garments performance is definitely optimized…

Often, as outdoor enthusiasts, we concentrate on the technology that delivers the attributes of waterproof protection and comfort of breathability.  More often however, we don’t take the time to consider what we are wearing beneath our outerwear.  But we should…because the base layer, insulating midwear, and outerwear work together as your comfort and protection system…  Remember the adage that we all learned early on in our climbing days, the one about the weakest link…  For this blog I am going to make the assertion that the weakest link is actually the base layer and mid wear, more so the assumption that we have all bought into the mainstream thought that synthetics are the best choice for breathability in garment systems which include a shell.

Wait a minute though we know synthetics are breathable right, I mean the Brands tell us that, and they have the tests to show it don’t they?  Well yes…and no…

Most times the test used to measure breathability in synthetics is called a RET test or Resistance to Evaporative Heat Transfer test. Evaporative is the main word here.  Synthetics do better with this test than wool because unlike wool, synthetics do not absorb moisture, making it easier for the evaporative process to occur… therefore achieving better test results.  Great, except where does that moisture evaporate to…remember we are in a closed system with the outerwear shell fabric still in place…a barrier that the moisture vapor has to be transported through…

Wool on the other hand transports moisture through its filament utilizing a physical process called sorption and then releases it through the process of desorption. In the process of desorption hydrogen molecules bang together, generating heat.  When heat is generated there is an increase in driving force.  It is the physics of driving force – the difference between the temperature inside of the jacket to the outer environment -  that transports the moisture vapor through the pores in your waterproof and breathable garments fabric.  The greater the temperature difference, the better the breathability! 

Conclusion:

Synthetics allow for moisture build up to occur underneath the shell garment slowly making it’s way through the pores that allow for the breathability…if you stop or get buffeted by wind you get chilled because the moisture that is close to your skin leaves you wet, clammy, and cold….causing conductive heat loss…

Wool absorbs moisture, and then releases it, keeping you comfortable along the way.  Most importantly the buffering that the wool filament provides allows for an increased rate of breathability when coupled with waterproof and breathable jackets.

So…if you want the best performance with your waterproof breathable jacket…layer with wool!