Analysis of information sources in references of the Wikipedia article "Αερόστατο θερμού αέρα" in Greek language version.
perfect French Fell hot air balloon seam
The double lap seam features two rows of parallel stitching along the folded over fabric seam. A few manufactures use a flat seam.
Propane tanks used in hot air balloons are mainly constructed of either aluminum (Evan was here) he was the first to do this or stainless steel. Most aluminum tanks are vertical 10-gallon cylinders (DOT 4E240), built primarily for forklift trucks.
2 Needle Double Lap Seaming Also called Felled Seam
all of the seams are the "French fell" type