I don't know if fusible batting could stand up to machine washing. Also, washing alone may not remove the odor; cat urine is just about the worst for persistent odor (that can return when the material gets damp).
What worked best for us with a bad cat accident was F.O.N. (Feline Odor Neutralizer). You would spray this on until the fusible is saturated, then let it dry naturally. You could test it on a small piece of the fusible first to make sure the fusible remains viable.