This is Warm and Natural (I'm sure they would be delighted to know that theirs is the preferred batt for mouse nests). Looking at the label, which says it doesn't need to be prewashed (but in this case it does), I found directions for washing the batt. Has to be done by hand; I imagine that the washing machine does an even better job of removing the cotton from the scrim. It has to be wrung out by hand but at least I could put it in the dryer. So the majority of the batt was saved and I have repositioned my other batts in what I hope is a more inaccessible space. And set a trap, baited with cat food kibble. Why use kibble? Because I've seen the little mice run out from under the cupboard, straight to the cat food bowl, steal a piece of kibble, then run back. Obviously, my cat is not viewed as much of a threat.
