Abstract: The present invention concerns a paper or board product with an improved tensile strength comprising cellulose fibres, one or more zirconium carbonate compound(s) and water-insoluble polyvinyl alcohol fibres, and a process for manufacturing such a product, comprising the steps of forming a combined aqueous suspension of cellulose fibres and water-insoluble polyvinyl alcohol fibres, and pressing it into a paper or board product, or pressing layers of water-insoluble polyvinyl alcohol fibres and cellulose fibres into a product having a sandwich-structure, and treating the product before drying with an aqueous solution of a zirconium carbonate compound by impregnating one or more of the surfaces of the product or the complete product with the solution.