I've felted with no soap, and with detergent, and with baking soda. It all seems to turn out the same. What seemed to help was adding some jeans, or tennis balls in a bag, or something like that to agitate it more. My washer is new, and it does some new-fangled agitation that is supposed to be less stressful on the clothes (just magic water-swishing). Well...it takes a long time to felt with it. I think the soda is to compensate for the hardness of the water????
Sweet Baby James-We're Bonding!