A system for controlling the residual moisture in pre-cured binder coated glass fibers. The moisture of the binder coated glass fibers is measured after the process water is extracted in a collection box. Based on the level of moisture found in the coated glass fibers, adjustments are made to the process upstream of the moisture measurements. The adjustments include, but are not limited to, adjusting the amount of water used to make the binder composition; adjusting the amount of heat applied to the binder composition as it is applied to the glass fibers and adjusting the vacuum conditions used to extract the process water from the binder coated glass fibers. Control of the residual moisture in the precured binder coated glass fibers helps ensure proper curing of the binder during the subsequent curing step.