The only window screen material that is ferret proof is METAL that is positively attached with staples, nail/screwed hold down strips, or factory type intallation. Plastic screen is NOT ferret proof. Velcro attachment is NOT ferret proof. Debi Christy Ferrets First Foster Home Practical & easy training, care, & maintenance articles available at http://www.geocities.com/ferretsfirst/ [Posted in FML issue 3801]