About the inner tube for Continental's limited edition tubular tire

the Tour de France Limited Edition,
compared to the regular Competition model,
the sidewalls are more supple, as I mentioned before.
I got a comment saying
"Could the inner tube be latex?"
It's plausible since it's a pro-spec hand-me-down,


but I had a customer ask me to stretch out the tire,
and on day three of using the stretcher Y,
it's barely lost any air, so it appears to be a butyl tube after all.