Hello @Rice_Guy, thanks for reply. There is no pressure rating. Here they cost about 7 cents each so I'm not expecting top quality.From the photo, this looks like an aluminum cap with a plastic liner. Metal provides excellent oxygen barrier properties, for oxygen it doesn’t get any better. The interior looks like a plastic liner. Plastic liners inside a metal screw insulated the acidic wine from touching/ reacting with the metal. It doesn’t get any better.
The inside looks threaded which lets one snug down/ deform the plastic to conform with glass imperfections. IS the cap pressure rated? Probably is at least one atmosphere. OK.
One more question: for one-liter bottles, they have both brown and green colors. Is one color better over the other for red wine? Green color, for some reason, is slightly more expensive.