a high - altitude balloon having prestrained gores made from an asymmetrical gore pattern . the invention includes the balloon , the method of assembling the balloon , and a table specially designed to implement the method . the method can be used to assemble balloons of varying shapes and sizes , within a determinable range of ratios of gore width to gore length . the method involves cutting and sealing edges of a pair of flexible plastic sheets along a straight edge of a table , then inverting the seam so formed until it is aligned with a curved index line on the surface of the table . the curved index line is longer than the seam created along the straight edge so stretching is required during inverting . successsively cutting , joining and inverting pairs of sheets in this manner produces a balloon with a plurality of symmetrical gores that give the balloon a predetermined shape when inflated .