Yes, that's PTFE aka Teflon.

Looks like you can use HDPE, actually. I think that's what it's usually shipped in, too. https://www.sciencemadness.org/whisper/viewthread.php?tid=15...

Well, HDPE would be way easier to manufacture there.

But people on your link are mostly unanimous:

"Quite often the caps are the weakest point. And as mentioned above HDPE bottles tend to sweat over time. I would vote against long time storage (years on end) of sulfuric acid in HDPE bottles."

They are not nearly unanimous.

> I have also a HDPE bottle of 98% sulfuric acid over a decade old without single hint of issue.

And they're talking about almost pure acid, which is not nearly what's going on in at atmosphere that's mostly CO2. Venus is probably not even as strong as drain cleaner.

Among the chief arguments for a balloon-based Venus station is that the high atmosphere doesn't have (much?) sulfuric acid, as the surface does.

So surviving H2SO4 isn't highly salient.

It doesn't take a lot of acid to cause problems over time. You still wouldn't want to use steel, as mentioned above. But yeah, you don't need Teflon either. Honestly I'm pretty sure I remember HDPE showing up in real proposals for Venus missions, which is why it was top of mind.