Update on the Bic pen. <br><br>Barrel and endcaps are made of polypropylene ( I checked with Bic) . I don't know the chemistry of pp well enough to know for sure that there is no reaction taking place but for two months the iodine has bee stored in this way and not yet weakened the tube.<br><br>Air Tightness. Well after chewing on them I wouldn't expect them to remain tight. Also I haven't subjected them to changes in air pressure such as would occur when sucking on them. I do know that in an earlier attempt to package these tablets I failed to get air-tight containment and everything in my kit turned yellow. I replace yellowed items and the container and haven't seen any yellowing from the tablets stored in the bic tube. I could probably gasket the caps with ptfe plumbers tape for a tighter seal but that doesn't seem necessary yet. I may find a different result if I took these to altitude thereby causing a significant pressure gradient. I could probably also get away with a dab of Krazy glue on the caps but that would certainly make it more difficult to get into the tablets when they are needed. <br><br>I will investigate further with organic chemists that I know. If there are any here qualified to inform on the interactions between free iodine and polyporpylene then please step forward. This form factor is the best that I have been able to find/devise and in this application volume is everything.<br><br>My wife suggested using the sample tubes that are provided for perfume. I haven't found one of the right diameter yet. These are glass and the cap could certainly be protedted by ptfe tape. If anyone sees one of these of the right diameter please post the brand name of perfume so I can try them out. As with the Bic pen the cap on these is a friction fit and may be subject to leakage at altitude. YMMV.