Air Permeability vs Breathability

The terms ‘air permeability’ and ‘breathability’ are often used in CBRN garment descriptions, but what’s not commonly understood is that they relate to different things.
Air permeability in textiles is the measure of the volume of air that is able to pass through the fabric structure under controlled conditions. 
Breathability is a fabric’s ability to transmit moisture vapour and conduct body heat outward through the material. Put very simply, breathable garments remove heat and prevent sweat build-up, which helps to keep the wearer comfortable.
As a generalisation, we can think of air permeability as the inward flow through fabric, and breathability as the outward flow, and whilst air permeable fabrics do tend to have relatively high moisture vapour transmission, a fabric does not necessarily need to be air permeable to also have some measure of breathability. 
The challenge for CBRN garment designers is to configure appropriate ratios between air permeability and breathability, while also achieving high CBRN protection within the garment. Today’s soldier and first responder want the assurance of comfort and enhanced wearability as well as high protection from airborne challenges.  
At OPEC CBRNe, we have developed a family of CBRN garments. Our garments vary in levels of air permeability and breathability as a response to differing risk environments. However, our overall goal remains to provide maximum CBRN protection by blocking CBRN challenges from the outside while simultaneously allowing air flow and enhancing comfort by allowing heat and perspiration to move out of the garment.