I knit a chemo cap for a friend of my old roommate. I knit it in an angora-wool blend, Classic Elite Lush. This is a very, very soft yarn.
The response that my roommate said she gave was that she was totally thrilled with this hat. Her comment was that most of the hats she has are acrylic (I don't know how soft acrylic they are) and that they are very itchy and uncomfortable. The angora costs more, but IMO (especially in a cold climate where warm hats are extremely important) totally worth it. It's gloriously warm and soft. After working with Lush for a long time (I made a sweater and a couple of hats with it), even the softest of acrylics just doesn't cut it.
The hat may need to be washed at some point, but I think rarely enough that handwashing would not be a big deal.
Also, if I ever need to make a chemo cap again, I'm going to try baby alpaca/silk. I don't remember what brand I have used for things in the past, but it is also incredibly soft and warm.
recent FOs: Shedir cap, Bricks of Atlantis, Pirates Hat, Citrine Socklets, Teddy bears, 1 entrelac sock
OTN: scraps blanket, Shedir for Teenie, Ice Serpent Hat
NIL: Qiviuk tam re-visited; weatherproof gloves; sweaters
My knitting blog: http://emilai333.wordpress.com/