That isn't quite true. Down breeds are naturally felt resistant. Generally those breeds are meat sheep.all wool will felt given the proper treatment. you need hot water, soap and agfitation. felting happens whent he cuticle (scales) on the outside of the wool fibers open which is caused by the soap and warm water. if then agitated, those open cuticles grab onto one anotehr and they form felt. I would not felt Merino, though as spun it is SO much nicer!