DUCT TAPE INDY FEDORA
  Hats are 100% high quality duct tape, except for decorator plastic wrap lining, and  pre-formed cardboard brim insert.
Duct tape in Raiders of the Lost Ark?
I think it's silver tape because it wraps around the corner of the post, is crooked and it's bunched up. There's some in the same spot on the other side of this bench that Indy is sitting on. Maybe it wraps around and holds the whole bench together.
This hat at the "Duct Tape Guys"
The secrets of the Raiders of the Lost Ark fedora!
This is the hat I bought on eBay in 2016 that was 2 1/2 sizes to big for me. I cinched it up, with a 2 1/2 sizes smaller sweat band, moved a 1/4 inch up into the crown front and rear, and I knew I had the Raiders hat. It's a Lock and Co. from Britain, I'd guess made in the 30's 40's or 50's, because the silk liner was sewn in. (The brim was too narrow.)
These two hats are the ebay Lock & Co, and a 3 sizes smaller Akubra Federation 4. I used the Akubra's leather sweat band in the cinched up Lock to the left.
2 1/2 sizes too big Miller "Harrison", base of crown shrunk to fit.
3 1/2 to 4 sizes too big, 2005-2008 Herbert Johnson Poet sold by Swaine Adeney and Brigg. Details in video.