Abstract: Fiber made of cellulose formate and fiber made of cellulose regenerated from cellulose formate. These fibers exhibit high tenacity and modulus properties, combined with improved values of elongation at break and of energy at break. Their elongation at break, in particular, is greater than 6%. Methods for producing these fibers. The fiber made of cellulose formate is obtained by spinning a liquid crystal solution of cellulose formate according to the so-called dry-jet-wet spinning method, the coagulation stage and the neutral washing stage which follow both being carried out in acetone. The fiber made of cellulose formate in a highly concentrated aqueous sodium hydroxide solution. The spinning and regeneration methods can be employed in line and continuously. Reinforcing assemblies based on such fibers. Articles reinforced by such fibers or assemblies, these reinforced articles being in particular tires.