My first go at needle felting. You start of with the wool above that can be teased apart. Lots of parallel strands.
Then the needle has a series of tiny barbs near the tip. You poke down through the wool and pull out. It drags bits of deeper strands back up across the nearer ones and thus binds the whole thing together.
This seems like a good analogue for cross-linking in polymers to make them more solid. You can see some of the cross-links in the yellow wool.
