I was science teaching at Naremburn Boys High (a small suburb of Sydney).
School holidays were coming up, and my headmaster allowed us to use the assembly hall as a balloon factory. 
Here, our School Science lab was converted to a planning and cutting room.
   The new balloons' size was dictated simply by the amount of film we had. At the rear of the bench is the roll of Aluminium coated polyester film. It was laid against marks on the table. We would cut 16 identical strips, (one for each gore ), change the marks and cut another 16.
  We used 3/4 mile, i.e. about 1.2 kms of material. The entire balloon was made from that single roll.
R to L. John Holmes, Ros Breillat , Garry Smith.
 
         
 

My tireless wife Pat lining up tape along a seam. These seams required tape on both sides.
   That added up to 1.75 miles, or 2.7 kms of tape. We then had 0.75 of a mile of ironing, to cure the tape.

There were no such things as Personal Computers then, to assist with the various aspects of design. Even electronic calculators had not appeared.