Re: Why doesn't air flow easily through the gaps between the fibers of clothes?

Ironically, air DOES flow easily through the gaps between clothing fibres.  
The resistance occurs only when the air collides with the fibres, or flows 
around them and produces drag on the leeward side of the fibre.  

The tighter the weave of the fabric, the more resistance it offers to air 
particles, thereby preventing it from flowing through the fabric at all.  
This is why wind and water-proof jackets are able to keep out the wind so 
well - because the nylon fibres are woven together tightly enough to keep 
the wind out.  Most of the research in this area has focussed on keeping 
air out and reducing the drag on cyclists.  

"Wind-proof" jackets will reduce the loss of surface body heat and also 
reduce the cooling effect of sweat evaporating from the skin by keeping the 
wind out.  Fabrics that let the air flow through them (like cotton and wool 
fibres) are often used for summer weight clothing that helps to keep you 
cool.  The new "cool-wool" is a thin, wool fabric that lets air pass 
through easily because the fibres of each thread are fairly large and 
loosely held together.  They reduce the drag on the wind and allow it to 
pass through easily. 


Cyclists search for clothing that does not let much air pass through and 
clings to their body tightly so as to reduce wind resistance (or drag) on 
them that can slow them down.  This is why they wear spandex and lycra 
clothing.  Here are a couple of sites dealing with the cyclists, clothing, 
drag concept.

 http://www.e
xploratorium.edu/cycling/aerodynamics1.html
 
 http://www.enter.net/~dlandis
/main.htm