Process and apparatus for non-invasive measuring of binder mix loading of glass fibers for monitoring production of construction insulation product, such as roofing and wall insulation. The process utilizes visible (VIS) and near infrared (NIR) spectroscopy; and, is particularly advantageous when utilized in an on-line production processing following binder mix loading of glass fibers and prior to curing treatment of the binder mix loaded glass fibers. Such spectroscopic analyses can be carried out on a static or moving support substrate. The blend is then conveyed to and through curing treatment to form insulation product. The blend is exposed to VIS-NIR radiant energy, and a radiant energy sensor collects resulting data as to absorption following penetration of the VIS-NIR radiant energy. The spectroscopic instrumentation is calibrated to determine to facilitate accuracy; and, can be used to verify load following curing. The amount of binder mix, in the binder mix/fiber blend, is adjusted if the blend is outside of desired loading specifications.