Stiff reinforcing for hood brim

Fabric shops sell stiffening.
Thin whipper snipper (brush cutter?) cord also works well.

Cheers

I like the whipper snipper idea, thanks

You want it to be a brim that sticks out a bit – flat rather than just a cord

I use this stuff you iron on, then remove the paper backing, then put a second piece of fabric and do the same, then iron the two pieces together. They sell different thicknesses – you want the heaviest one.

But that's not real stiff so there's probably something better

cut out action of a plastic milk jug. Free, and someone on this site did it a long time ago to make a brim on his Driducks

The plastic ks great for other similar uses too

I like the milk jug idea, if it will have a brim like a baseball cap. If you'd prefer that the brim has a hoop (for packability or something), I've read that Delrin (acetal) rod is the best. It is stiffer than nylon (like the whipper snipper line), but not brittle like fiberglass rod. I don't know a source for small diameter Delrin rod, though.

Whipper snipper cord is usually a co-polymer. Much tougher and more flexible than nylon and Delrin.

Cheers
Edit: weed eater, string trimmer, whatever. As Steven said.

Just a guess, but I think Roger is referring to a "Weed-eater" or "weed-wacker", a trimmer with that blue plastic thick "line."

I've had success making hat brims out of cuttings from those 1 lb yogurt containers- they are just about the right curvature near the top of the container for a brim.

They've worked very well for the cycling caps that I've made, which are just slightly bigger than what I would use for a jacket hood.