I think the fusible is used with the understanding that it will be washed - it softens right up.
The stiffness is part of its appeal - no shifting of the layers when quilting.
I've used it on lap quilts (~72") and I loved the way it worked out.
If washed now, it shouldn't pucker any more or less than with regular cotton batting - based on if you pre-washed the fabrics - top and backing, the density of your quilting, etc.
Mind you, the puckering I'm talking about it is a little bit of crinkle.
The quilt top will NOT become all distorted if washed, if that was what you were thinking might happen.
Last edited by MTS; 10-24-2012 at 04:56 AM.