I had the same problem and my iron is brand new...I was thinking of just using non fusible for my next one and back it with muslin. The other problem I had was sewing directly to the batting..really got caught up in my needle and foot..I think the muslin will help that too..or a better fusible..The one I used was June taylor..the only one available at the store I was in.I also never prewash, but do not think that is the problem. I will be watching with interest, as I have many requests to make these bags too