Weeee! I just got to inspect something very cool here at Costume College in LA. In one of the lectures the instructor brought a vintage Quianna Knit gown in made by the designer who specialized in Bias cut gowns - Charles Kleibacker. It was my first time ever seeing or handling this fabric in person and I'd say with 99.9% certainty this is what the Leia ANH costume is made of. I know it's been a speculation in this forum for some years now, but after seeing it in person I'm more certain than ever! I'd even say that the version of this gown that was on display at the Star Wars exhibits is made of this same knit Quianna. It looked the same. Sadly, we really don't have anything like this now. I think the two fabrics that are closest are the polyester knits we've been using for fan recreations, as well as nylon knit swimwear fabric (so long as it's not too shiny, and has a fluid feel... not too stiff). Swimwear/dance wear nylon has a very similar feel because the quianna knit is also nylon. Another thing that was interesting about this lecture, it turns out that Charles Kleibacker would flatline the Quianna garments with the same quianna used on the outside. It was the only way to keep the drape and flow from changing. Again, just like the Princess Leia dress construction! I inspected the way he sewed his hem, and it was the same as the Leia dress hem is sewn. The raw edge of the lining quianna and outer quianna folded up together as if they are one piece, and loosely blind hem stitched by hand so it is not seen from the outside. See, learning about historical costuming really does help us understand all these wonderful Star Wars garments!