Blends of chain-extended reactive extruded recycled PET (RER-PET) and virgin PET were fed in injection stretch blow moulding (ISBM) process. The RER-PET blends have different RER-PET concentrations and RER-PET have different pyromellitic dianhydride (PMDA) chain extender concentrations. RER-PET composition and percentage in the blend were used as process variables. The resulted ISBM bottles were tested for burst pressure, top load, liquid permeation and carbonation loss. The experimental results were used in an optimisation process aiming to identify the best blend composition that produces best bottles properties. Models were fitted and statistically analysed to represent the bottles properties in the optimisation calculations. Two optimum points were found in which highest chain extender concentration in RER-PET were favoured. The optimum points showed different optimum RER-PET concentrations in the blend. The first optimum concentration is 20% RER-PET which resulted in best burst pressure and top load resistance. The second optimum point with RER-PET concentration of 29% produced minimum liquid permeation and carbonation loss. The results of the optimisation procedure are beneficial in identifying the possibility of the use of RER-PET for bottling application.