The original De Vere bellows seemed thicker than they are, and they aren't heavy. They are back in the UK so I can't give a better uea or photograph a cross section.
The rigidity seems to come from the way the three layers and stiffeners are glued together. They were tatty and leaked when I bought the camera in 1976, and I had some bag bellows made by Camera Bellows who had made the originals so had the patterns. The camera is a whole plate monorail with half [late & 5x4 backs and the bellows were only just usable with the 5x4 back.
The cloth I'm using will make the thickness slightly less, and lighter, but still as rigid so I'd expect the bellows to compress more than the old ones. That's based on the two other sets I've made so far.
I guess I could glue up some off-cuts tomorrow & measure the thickness, 2& 3 layers of cloth.