Used to fab all my own exhaust as we work on a lot of orphan cars with no kits available. Long before there was the plastic kits to make a prototype I used defroster duct and filled it with foam so it would hold its shape to transfer to steel tubing. Picture of a 57 Studebaker Golden Hawk home made header. Tubes are large diameter to go with an engine with a blower. When the foam sets the tubes are very rigid.

[img]https://i.postimg.cc/PCNw1pyq/57-Golden-Hawk-Headers-016.jpg[/img]

[img]https://i.postimg.cc/qN9znmgm/57-Golden-Hawk-Headers-017.jpg[/img]

[img]https://i.postimg.cc/Z9t50CD2/57-Golden-Hawk-Headers-005.jpg[/img]

Evan