Description from Knitty.com:
This is a non-intuitive sweater, I think. Pairing a laceweight mohair and a slubby, silk-and-cotton tweed is not standard yarn store practice, and I felt a little dubious about it myself at first. But knitting one strand of each together results in a wonderful fabric with the heft and durability of the cotton but with the kitteny softness and vivid color of the mohair.
For pure pleasure, the cowl neck is knit of the floaty mohair alone, which brushes deliciously against the neck.