Here are the details.
The cable is best seen without the flash, but that makes the image a little blurry.
This image shows the true color of the yarn and gives a better idea of the shape of the hat.
Yarn: The "Alpaka" brand 100% alpaca yarn that is sold at A.C. Moore. Approximately 1.5 skeins (each is 110 yards). This is a sport weight yarn comparable to the knitpicks Andean Treasure.
Pattern: I used the DNA cable from HERE and instead of inserting it into the scarf design with a seed stitch border, I did a four stitch stockinette border on either side of the 20 stitch cable pattern, with the first stitch slipped at the beginning of each row, and the last stitch always knit (on both RS and WS). I used US size 3 needles instead of US size 5, and did five repeats of the pattern. This number of repeats is just the right size for most adult heads. I used kitchener stitch to graft the ends together (you can use a provisonal cast on if desired). This works pretty well because it creates one continuous circular DNA chain and the graft point is nearly invisible.
After knitting the cable band and grafting it together, I picked up 90 stitches around the band using a US size 4 16 inch (total length) pair of circs (I think picking up the end loop of each slipped stitch should give you 90 stitches, but if you are one or two off, just increase those into the next round). Knit in stockinette for about two and a half inches, then begin decreases as described in the small size of this pattern. Switch to DPNs when there are too few stitches to use the circs.
This hat is particularly appropriate as a gift for anyone who works on bacterial genetics, since the cable creates the circular genome and/or plasmids characteristic of prokaryotes.