Tray blanks were moisturised to study the effect of different blank moisture content levels on forming behaviour and mechanical properties of paperboard tray packages. The blank moisturisation was done by spraying water to the blanks before their three-dimensional (3D) forming. The trays were 3D formed by press forming or deep drawing. Visual quality and punch force values were used as indicators to evaluate the forming behaviour of the trays. The mechanical properties of the trays were investigated with compression, torsion, and storing tests. A high blank moisture content reduced the punch force, and the elevated blank moisture was connected to a possible blistering effect in the 3D forming of coated paperboard. The compression test results indicated that the blank moisture content had only a minor effect on compression strength of the trays. The torsion test results linked a high blank moisture content to increased torsional stiffness in the trays. The storing tests yielded measurement uncertainties with the deep drawn trays while the trays press formed with a low blank moisture content showed improved dimensional stability. The blank moisturisation was concluded to enhance the torsional stiffness of 3D formed paperboard tray packages. A sufficient moisture escape during the 3D forming of coated paperboard was deemed necessary to mitigate a possible blistering effect to the coating.