The test procedure used is ASTM D4603. The solvent system used is 60% phenol/ 40% tetrachloroethane. The PET concentration is 0.50% and samples are analyzed at 30°C. The test can be run on resin, film, preforms and bottles. Corrections are made for samples if they contain >1.% additives or colorants. It is important to know the level of additives present when submitting a sample for analysis. PTI uses Rheotek equipment to measure IV . SIV data reported to the customer will be measured at a single concentration to obtain the inherent viscosity. The intrinsic viscosity is mathematically calculated from the inherent viscosity using the Billmeyer Equation.