I felt knitted wool often for felted slippers and purses. The felting occurs in the washer and you will be able to tell by the amount of shrinkage and there should be no loose threads when felted properly. Knitted felt is air dryed only. Even with 100% wool it can take 2 or 3 washes to get the desired felt. You do not want to be able to see any original woven lines (warp & weft) of the fabric. I have a sanitize cycle on my front loader that works well. Lots of agitation and heat is required which means the longest cycle with the hottest water that you have. Throwing towels in your felting wash load also creates more agitation. I always put towels in. My friend and I have knitted the same slippers out of the same yarn. Mine felt perfectly. She has a different washing machine and it does not felt nearly as well.