I was recently knitting something with some yarn that was 85% wool/ 15% silk. It said hand wash on the label. I wanted to see how or if it would felt so I knit a swatch and tossed it in the washer and dryer with a load of laundry. It didn't do a thing..did not felt at all. I've heard of other yarn that was supposed to be washable wool that felted a bit. I seriously doubt it will do anything, but best thing to do is make a swatch and test it.
When asking questions ALWAYS post the name and a link for the pattern if you have it.