Fusible web is an adhesive. That's all it is, a hardened glue substance that is softened by the heat of an iron and adheres to the surfaces on either side of it. When it cools, it again turns solid and holds the two things together. It does not wash out, nor is it intended to. That would defeat the purpose.
Are you thinking of water soluble stabilizer perhaps?
Last edited by ghostrider; 07-20-2012 at 08:36 AM.