The invention relates to organic fiber-based products and a method of manufacturing such products. According to the method, the fibrous raw material is milled together with a fire-retardant agent to a desired degree of defibering to the end of producing an at least essentially fire-retardant product. According to the invention, the fibrous raw material is admixed with at least a portion of the amount of the fire-retardant agent to be used, after which the material is milled to a desired degree of defibering using a refiner capable of exerting a milling action. Accordingly, when making a product suited for use as thermal insulation, 1/4 - 1/2 of the fire-retardant material is introduced to the fibrous base material prior to defibering in anhydrous form and 1/2 - 3/4 of the fire-retardant material is introduced to the fibrous base material after defibering in hydrous form. According to the invention, recycled paper can be used in the production of an at least essentially fire-retardant organic fiber-based material in which the anhydrous component incorporated therein swells during moisturizing, binds the fibers to each other and thus achieves a structure free from self-compressive settling.