This article was just posted in another section of the RPF. #1 on the list is the ANH Skywalker lightsaber. It features some quotes from Roger Christian. In this brief interview he says the grips were rubber.
https://www.thrillist.com/entertainment/nation/greatest-movie-props
Personally, I don't think there is any debate about what material the grips were made from, but I just find it interesting how the story changes sometimes.
He did say that-- but he could have been talking about a cast stunt from ESB or something.
For my money, the t-track was rubber. The way it bends on the ANH E-11 is all the evidence I need. Rubber can do a lot of things as it ages depending on its make up. It can harden, it can flake apart, it can warp... that explains most of what we've seen.
That said, I think that the post ROTJ sabers made by Bies used metal grips. Whether they were a metal version of the same draft excluders or something else, he won't say!
I'm amazed there were so many (did he make the tube fighting stunt from ANh?) And that there were so many kinds of the strip...
I didn't read they were rubber, I just always thought they were soft given how they rolled into the holes on the barrel.