Abstract: The invention relates to a process and composition for binding of a particulate or fibrous substrate, in particular natural particles or fibres such as for example wood particles and fibers, but also other natural fibers such as straw, flax, grass, straw, hemp, bagasse and bamboo. The current invention describes the composition of a cheap binder that can bind particles and fibers in a fast way, resulting in substrates that have the required mechanical properties. The binder has a good sustainability so that the end product also has an improved sustainability profile. Furthermore, the new binder composition will make the resulting substrates (composite materials) flame retardant.