Linen has been the favorite painting surface of oil painters for centuries. It is much stronger than cotton canvas, lasts longer, and has a smoother, less absorbent surface.
Some other reasons to use linen: growing flax requires much less pesticides and herbicides than growing cotton. In fact, my 13 year old son has done some research and found that just growing enough cotton for a pair of jeans and a shirt uses about a pound of pesticides and herbicides! It is one of the most heavily sprayed crops there is. As an artist and someone who is very concerned about the health of the environment, this has given me the motivation to convert to painting only on linen when possible - for oil and acrylic linen is great. I will need to look into non-cotton options for watercolour paper. I am currently using up the last couple of cotton canvases I have, and have begun making my own linen panels. (see images bellow.) It is more expensive, but well worth it.
The flax seeds, as most are aware, are amazingly healthy, and are used for many purposes. The cloth is made by soaking the stems in water for about a week, until they start to rot. They are then put through various processes to separate and clean the fibers from the unwanted portions of the stalk. For more info. on the linen making process, please go to Wikipedia, where there is much detail on the methods and history of this amazing plant. If you are an artist, please try linen!