I made up this hat using a yarn I picked up at a yarn and fabric exchange a couple of years back. I have no idea what it is, but it's quite nice. A bit difficult to work with, as it's made of of two strands of white yarn, and one squiggly strand of pale yellow that was almost like a string, wrapped loosely around the other two strands. It made for an interesting texture, but tended to get missed by the hook as I worked.
For this, I used 2 strands together on a 6.50mm hook. The main part of the hat is done in basic double crochet, with the last several rows done in alternating front and back post double crochet. With this yarn, using the two strands together resulted in a very squishy feeling texture that's quite warm and cozy.