Content with JR

J2 and JR refer to the material’s sub-grade - its fracture toughness - which is measured in joules [J] of a material’s toughness at a particular temperature. J2 is a material with a minimum of 27 joules at -20C while JR is a material with a minimum of 27 Joules at +20C (room temperature). A JR material is normally used in an internal environment whereas a J2 is for external use.
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