There's little doubt Idemistsu is using a predominately 4cSt GP III base oil with a VI in the 120 to 135 range.
How they acheive the ultra high finished 221 VI is by using one of the new very high VI polymethacrylates (PMA) branched or star type polymer thickeners.
How they acheive the ultra high finished 221 VI is by using one of the new very high VI polymethacrylates (PMA) branched or star type polymer thickeners.