The yarn I picked was DK and the whole project took less than a skein, surprisingly. I had to adjust pattern to suit a thicker yarn than the fingering called for. For a 23” circumference head I cast on 120 inches of the brown worsted with # 5 needles and knit 7 rows of 2x2 rib. This grips the head well without being tight. I used a couple of rows of white to simulate cranial bone, then started pink, beginning decreases after 20 rows and following pattern from there. Worked out great.

For the I cord I used #3 needles. It took about 24 feet per hemisphere, accomplished in about a week of evening TV watching.

I used a cheap foam head form I got online to put the hat together. The concept was great, could poke pins right in. But it was too small as you can see, so I stuffed it with fiberfill to 23”. I used a tapestry needle to attach Icord, tacking the loops to each other and anchoring them through the cap every inch or two.
I’m delighted with the result; hope my college-bound granddaughter gets as big a kick out of it as I did. Fun project!

Since I wrote this I’ve made 3 more for people with 1 left to do. Gotta tell you that’s about 3 too many. Pretty brainless (hah.) People seem to love it, though.