novel polyester for the packaging of perishable comestibles , e . g ., as bottles for still or carbonated mineral waters , is a polyterephthalate having an intrinsic viscosity ranging from 0 . 65 to 1 . 05 dl / g and a density of more than 1 . 38 , comprising 92 . 5 to 98 . 5 % of ethylene terephthalate recurring units and 1 . 5 to 7 . 5 mol % of recurring units of at least one polybasic acid and / or polyhydric alcohol comonomeric crystallization retardant , the di - and / or triethylene glycol content thereof being less than about 3 . 5 mol % per mol of diacid radicals present in the polymer chain , said pet also having a residual acetaldehyde concentration of less than 1 . 25 ppm , with acetaldehyde being reformed therefrom at a rate of less than 5 ppm / hour , at 220 ° c ., and said pet being devoid of visible crystallization in an at least 4 mm thick test plate shaped in a mold cavity from a melt thereof .