I happened upon a Fenwick ff80 B series serial number (1960s I believe) that needed a guide replaced.

Removing the old guide, I find that the gold tipping is actually a mylar like material and the chestnut thread is overwound (with a space between the threads) over the mylar.

Anyone familiar with this material or technique?

Although there's no way the repair is going to match the patina of the original, I'd like to stay true to the original if I can. Plus it's a nice look and I'd consider it for other builds in the future.

Archfly, I haven't done it in a long time, don't recall the details, and can't quite picture the use of mylar on this particular rod. Still, I think it is easy enough to replace the mylar as well, but only a good idea if it is damaged or blistering away from the blank. Perhaps you could comment from more recent experience. If I ran across that situation now, I would take the lazy easy route and remove all the mylar and just wrap. But retaining the original look is a good idea, too, so maybe the OP needs some info on mylar underlayment. One little advantage--or at least making a virtue of necessity--is that the mylar protects the blank from abrasion by a stressed or wiggly guide foot. So I would definitely inspect the feet if guides are reused, and check the condition of the mylar and blank where the guide foot sat.

I think Clemons (or someone) sold self adhesive Mylar tape, Barlow's Tackle has "lure tape" in solid colors that might work. Amazon has various self adhesive Mylars.

Between fly tying suppliers and craft stores, or among automotive products used in pinstriping, I'm sure you can find something suitable. But it makes perfect sense: if it ain't broke don't fix it. Would enjoy seeing before and after pics.

Racking my brain... we used to do the cool mylar thing when I was a kid, I can't recall glueing it to the blank....thinking...thinking...

Stupid non rod builder question, but was Mylar used on rods or was it metal foil of some kind and the term mylar is used generically to describe "shiny stuff?"

Or both...

Thanks in advance for the enlightenment.

My old rod building buddy had mylar in sheets about the size of a note book paper.
It was gold on one side and silver on the other.He would cut a piece a little bigger than
he needed and then coat the area where the mylar was going

with thinned head cement.Then he would put the edge of the mylar in the cement and take a dry brush and paint it around the blank. Trim it with a razor blade and let it dry,and wrap the rods the next day.
That was in the late sixties and early seventies.
Mylar went out of fashion about then,in our area anyway.