Fabric Tech 101: Ventilation
Ventilation is a critical component of comfort in clothing in managing both heat and moisture and is primarily focused on increasing airflow through out the garment.
Understanding Diffusion: A key part of passive methods of transporting heat and moisture is diffusion. The speed of diffusion (or transfer) of moisture or heat proportional to the difference in temperature or humidity. The bigger the difference the faster heat travels - this is called Newton's Law of Cooling. For example, wet towel will dry faster in arid Arizona than humid Hong Kong - and that’s due to the differences in humidity.
Moisture and heat move from hot and or humid areas to cool and dry areas naturally and evenly.
A hot water molecule has lots of energy and is moving very quickly. When it hits a cold water molecule it transfers some of it’s energy just like billiard balls. The result is two warm water molecules.
Heat Transfer: In order to dissipate heat we can use any of three methods: Conduction (through skin contact), Radiation (through light), and most commonly, Convective heat transfer which is through moving air.
How it works: Heat transfer is fastest when the temperature difference between our body and air are greatest, however, the space between our skin and shirt for example creates a micro-climate that tends to be warmer and more humid that the outside air. To accelerate cooling, we want to circulate, cooler, drier air throughout the garment.
Fabric traps heat and moisture in the thin pocket of air between our skin and our clothing known as a microclimate. The temperature and humidity of this microclimate are what we react to in terms of feeling hot, clammy or cold.
Moisture Vapor Transfer:
How it works:Our body naturally expels moisture, and increases this as our body temperature elevates as a cooling mechanism. Sweating works by what is called “Simultaneous mass and heat transfer”.
First, our body expels heat releasing sweat which carries within it thermal energy (heat), then through evaporation liquid sweat transforms into moisture vapor. This phase-change absorbs heat from our body.
Second, because it has turned to a vapor, it can leave the body and carry the excess thermal energy with it in the form of steam.
By increasing airflow exchange, we accelerate both evaporation and we can transport that steam faster, and accelerate evaporation
Evaporative cooling works by taking heat out of our body in terms of liquid sweat, converting it to steam with body heat, and allowing that steam to flow or diffuse away from our body. This is known as “simultaneous heat and mass transfer”.
Examples: We use a variety of techniques to increase airflow in our garments to provide ventilation:
Body Mapped Seamless Ventilation: The Atlas Tee uses seamless variable knitting to enable a looser, more open knit structure in the underarms to increase airflow
Knit Structure: A pique knit structure has air gaps allowing air to flow easily through the shirt. The Apollo allows 19x more air flow than a traditional woven fabric
