Not teflon tape, but...

I am currently researching the foil-lined seals from the top of orange juice bottles. No, really. Here in New Zealand, orange juice is available in 1 litre and 3 litre plastic bottles. There is a lid on the bottle. Underneath the lid is a dense foam seal which is heat-welded to the mouth of the bottle. The seal is about 1" in diameter, with 3 small tabs around the circumference. The seal is peeled off and discarded when you want to open the bottle, and of course the lid can be screwed back on afterwards.

The seal material is dense foam, about 1mm thick, with a foil underside. I think the foil is coated with polythene. I took a 10mm punch and punched a circle out of the seal, and inserted it into the lid of a small vial. The vial lid already had a small disc of dense foam as its original seal. My premise was that the foil would be a good block for iodine, even though the polythene layer might absorb some. I assumed that the existing foam disc in the cap would add more spring pressure to the foil/foam disc and allow an even seal around the mouth of the vial.

I did this about a month ago, and the result is pretty good.

The first time I re-packed the tablets (I am using Potable Aqua) I used only the original foam disc seal in the vial lid. It soon went brown, and other things that were packed next to the vial started to become affected by iodine vapour (e.g. the chrome top on my mini BIC started to corrode).

So, I got a new lid with a new insert and added the punched disc from the orange juice seal. For your delight, ladies and gentlemen, I have just now removed the cap and examined it. It is true there are some brown circles which mark the outline of the mouth of the vial, but! The original foam insert can be seen at the edge of the new foil insert, and it is still white. Iodine vapour would make it brown, and it would be obvious. I will call it success!!

The only improvement I would make is to use a bigger punch. The mouth of the vial is about 10mm, so my disc has to be placed carefully on top. The inside of the lid is about 11mm or more in diameter (to accommodate the screw threads on the vial) so it is possible that the foil seal would move wrt to the mouth as the lid is tightened.

I think that a disc of heavy foil would also work, with the springiness of the original insert behind it to give a good seal. I think that teflon tape, even though it is impervious to the iodine vapour, would be too fiddly to use, and would be destroyed by the action of screwing down the cap.

Whew! That was a long post. I hope it made sense.