Paper or paperboard product comprising at least one ply containing high yield pulp and its production method

A method of producing a paper or paperboard product having at least one ply comprising high yield pulp (HYP), comprising the steps of:

• providing a furnish comprising at least 50% of high yield pulp (HYP) of a total pulp content in said furnish, said high yield pulp being produced with a wood yield above 85%;
• dewatering the furnish to form a moist web, pressing said moist web and drying said moist web to a dry solids content of at least 50-70%;
• densifying the moist web to a density above 600 kg/m3 in a single press nip of a paper machine at a temperature above a softening temperature of water-saturated lignin comprised in said high yield pulp to provide a paper or paperboard product, containing at least 30% high yield pulp (HYP) of a total pulp content of said product, wherein the temperature in the single press nip is in a range between 160° C. and up to 216° C., and a press nip dwell time is about one second;
• and
• drying the web to a final dryness after the densifying step.