I bought an '87 Prelude, 2 months ago, at a yard sale, rode it for a week; then moved south to Letour Luxe land. I've now returned to Prelude land, for one more week, before returning to México. I'm going on a group ride in a few minutes, and in preparation, replaced the tube in the rear tire, which has a bent internal stem on the presta valve. It's also yellow, and translucent, something I've never seen before. Now I've been cycling for 50 years, but always on entry level bikes, until now. It's a Schwinn Dura Sport. Made in Japan. Inside of a Schwinn Super Record tire, so probably original. Were these things common back in the day? Can I treat it like a latex tube when it comes to patching it?

If it is transluscent and yellowish in color, It's most likely a latex tube. People buy them because they were quite a bit lighter than regular butyl rubber tubes. I've used them before when Speciaized sold them in the 80's and 90's. I did not find them any more fragile than regular tubes and were just as easy to patch when punctured. Only difference I noticed was they do not hold air as long as butyl tubes as they are more porous, so you have to pump them before every ride for sure.
They are still available out there (From Michelin), but are sometimes hard to find as lighter butyl tubes are now being made that get closer to the weight of latex tubes, so not many bother with them (because of higher cost) anymore. I quit looking for them too as just I use Vitorrias lightest tubes (55g) that seem comparable.

Chombi

Thanks