You’re articulating what I’m thinking much better than me lol. I’m definitely starting to think it might have some sort of base frame/ layer. I’ve mostly been going at it from the leather working perspective; finding the right flat pattern that translates into the 3D shape. Best example of this is around the outer corner of the eyes. The forehead piece is shaped so that it is cinched to begin forming the browline, and the rest can be shaped by wet molding.Looks great! The cowl seems like it's the hardest part, since it's a mix of more organic shapes with some angularity.
If I can offer some comments, looking at this pic:
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I don't have much experience in costuming of this type, but it seems to me that the cowl may be sculpted and cast out of something semi-rigid like urethane or latex, then a thin "leather" layer (I'm not so sure it's actually leather) is shaped over the top and stitched directly to the under part, rather than just using stiff leather stitched together like you're using. Or maybe the whole thing is just moulded rubber, and it's just simulating that it's made of leather. The stitching looks more like machine stitching, which is another reason I think either the leather is thinner, or it's not actually made of leather.
Just now, I found this Etsy seller's Battinson cowl - I'm not affiliated with them, it just came up in my search. I don't know if its construction is accurate to the movie (they boast that the movie's designer commented on it and said they "nailed it" but I don't know if that's true). But it looks pretty good, though still not entirely accurate. Maybe the pics can offer some assistance in your design. They say theirs is made from urethane:
The Batman 2021 2022 Battison Cowl Robert Pattison Matt Reeves | Etsy
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Don't get me wrong, the cowls you've been doing look great. I think the black ones in the pic you just posted look closer to the cowl that the tan leather ones. If you do continue with the thick leather, I'd suggest a "butt stitch" would look more like the stitching on the movie cowl.
That Etsy mask looks really good, and I found another accurate looking 3d model. The problem I keep running into is getting an accurate flat pattern off the screen. I’m just gonna have to keep working on my Illustrator skills.
The tan cowls are my early experimental designs and the black ones are modified versions of This pattern using different leather thicknesses so I think I’m on the right track with those ones but I’ll try using the butt stitch.
I just finished a promising foam pattern and restocked on leather so I’m going to work on that over the holidays.