Linen is a fibre made from flax. Unlike Cotton, it's harvested from the stem of the plant and loved by many cultures for its ability to keep the wearer dry and cool. As a hardy plant it demands very little in the way of intervention (the UN notes it needs 13 times less pesticides than even the humble potato) but its more labour intensive process to get from plant to fibre keeps it from overtaking cotton or manmade alternatives (it accounts for approx 1% worlds fibre consumption.)