Cabela's use to sell these. They are a light weight down jacket liner that is made to fit under a heavier jacket. Similar to the jacket liners that are made to button into an Army field jacket but made out of goose down. I've wore out two of them over the years and would like to find some one who is making them. Cabela's doesn't show them anymore.

Campfires tear them up by shooting very small pieces of hot rock onto the nylon taffeta and that starts a pin hole, then the down starts working it's way out of the pinhole.
I see down can be bought on E-Bay bulk. I guess as a last resort I could buy some of that and find a talented seamstress (seamster?). and see if she, he, could piece them back together but I'd buy new if I could. My sewing talents end with making knife sheaths.

Eddie Bauer sold them in the 60s, then starting selling everything else.

https://www.decathlon.com/collections/mens-down-jackets

Just buy a new thin jacket and save yourself time and money.

Yes, or maybe a down vest, and wear a cheap shell over top when sitting around a campfire.

I had two that were from Herters back in the early 70s. Nice and warm, but, they would get a hole in them just looking at a patch of briar. Only so many duck tape patches and they had to go.