Description Castrol Magna ™ PR (previously called Poly ™ XN) series is a light bodied, naphthenic type rubber process oils. These are formulated from carefully selected mineral oils to increase the rubber's processability. Application These oils are essential components in the processing of rubber for the manufacture of tires, inner tubes, mats, shoes. molded and extruded rubber products. Benefits Castrol Magna PR 40 offers: Improved elongation and tear strength of cured stocks. Low grinding temperature due to the improved plasticity of the rubber. Shorter grinding time and power consumption due to faster dispersion of components. Better aging properties in rubber products.