Fiberglass vs. Fabric

Ok, I just finished reading Tony Bingelis's "sportplane builder"
section on covering a wooden plane with fiberglass instead of the
intended fabric. Has anyone in this group ever done this or some who
knows someone who has done this? I'm building a wooden place that
calls for
a fabric covering. I've tried to do as much homework on this subject
as I can but still can not come up with a weight difference between
fabric and a thin coat of fiberglass. I know that the fabric is not
structural so why can't I subsitute a lightweight fiberglass for the
fabric?
Any feedback?
Lou