The present invention relates to a method of manufacturing a cellulosic film (cellulose film), particularly a cellulosic food packing film, especially a detectable cellulosic film, which cellulosic film comprises detectable particles incorporated therein, as well as to the cellulosic film thus produced and to its applications and usages (i.e. its use).

The present invention relates to a method of manufacturing a cellulosic film (cellulose film), particularly a cellulosic food packing film, especially a detectable cellulosic film, which cellulosic film comprises detectable particles incorporated therein, as well as to the cellulosic film thus produced and to its applications and usages (i.e. its use).

It is an object of the present invention to provide an ultrafine cellulose fiber-containing material having favorable re-dispersibility, which can exhibit excellent thickening properties after it has been re-dispersed, even after long-term storage. The present invention relates to a cellulose fiber-containing material comprising cellulose fibers having a fiber width of 1000 nm or less and a di- or more-valent metal component, wherein the content of the cellulose fibers is 5% by mass or more with respect to the total mass of the cellulose fiber-containing material, the content of the metal component is 0.5% by mass or less with respect to the total mass of the cellulose fiber-containing material, and when the cellulose fiber-containing material is processed into a slurry having a solid concentration of 0.5% by mass, the pH of the slurry is 4 or more.