ISO 29221:2014 specifies a method for the determination of the plane-strain crack-arrest fracture toughness, Kla, of polymeric materials by using a side-grooved, crack-line-wedge-loaded compact tension specimen to obtain a rapid crack run-arrest segment of flat-tensile separation with a satisfactory crack front. ISO 29221:2014 employs a static fracture analysis determination of the stress intensity factor at a short time after crack arrest. The estimate is denoted as Ka and when certain size requirements are met, the test result provides an estimate, termed as Kla, of the plane-strain crack-arrest toughness of the polymer. The specimen size requirements provide for in-plane dimensions large enough to allow the specimen to be modelled by linear elastic analysis.