The invention relates to a method for producing a bio-PET polymer comprising the following steps: Step A) providing at least one diacid compound, comprising a terephtalate compound; Step B) providing at least one diol compound, comprising monoethylene glycol; wherein —at least one of the terephtalate compound and/or the monoethylene glycol is obtained from at least one bio-based material, and —at least one of the diacid compound and/or the diol compound further comprises at least one crystallization retarding compound; and Step C) copolymerizing a mixture of the diacid compound and the diol compound to obtain a bio-PET polymer comprising diacid units and diol units, comprising up to 7.5 mol % of unit(s) corresponding to the at least one crystallization retarding compound, based on the total number of moles of diacid units contained in the bio-PET. The invention also relates to a method for producing a bio-PET packaging element, comprising the following steps: —performing the method described above; and —Step D) converting the bio-PET into the bio-PET packaging element.