My favorite chemo cap yarn is Debbie Bliss Cashmerino/Rowan Classic Cashsoft (they have the same fiber content). Very soft and comfy, and machine washable. I've also made a few out of GGH Bali
, which might be better for a warmer climate since it's cotton/acrylic. The person I made them for loved them to pieces -- she asked me to make more of them. :D I think it's especially nice because you can make a hat from one ball, and it somes in sooo many colors.