I have an old fuse box from the 50s or earlier that accepts type TL fuses. I recently discovered two of the insulating washers inside of the sockets were missing. I took out a washer from a good socket to examine it for replacements. It appears to be a fiber washer, and I found a very similar fiber washer at the hardware store. My question is, should I use the new fiber washer or is there some other material washer I should use? Perhaps neoprene. Also, are "fiber" washers made from fiberglass, paper, or something else? Will they hold up under the heat and current of a 30 amp circuit? Thanks.
Some are paper and some are mica on old panels I have worked on , I believe I may have seen some fiberglass ones but not positive. As long as it is an insulator (not conductive) you should be fine. Your fuses don't get hot really when the blow that's the highest temp and this should be well below 451f the ignition point of paper.