Abstract: A series of polyester and vinyl ester based insoluble binder compositions for use with fiberglass are provided. These compositions are comprised of cross-linkable unsaturated resins used in tandem with various azo initiators. The compositions are capable of thermally curing; creating a water and organic-insoluble binder exhibiting good adhesion to glass. These thermally cured binders are able to provide similar fiberglass tensile strength to the conventional dibenzoyl peroxide containing compositions, while exhibiting improved retention of whiteness over time.