The invention relates to a method for producing a fiber based product, wherein the method comprises the steps of: a) applying a binder composition over a at least one surface of at least one fiber based substrate; b) determining the distribution of the applied binder composition over the en-tire at least one surface of the at least one fiber based substrate; and c) based on the determination in step b) either accepting the treated at least one fiber based substrate for the production of the fiber based product or rejecting the treated at least one fiber based substrate from the production of the fiber based product. The invention further relates to a method for producing a binder composition, to a binder composition and to a fiber based product.