Potable Acqua is sealed into the half length Bic-Stick pen with two of the end-caps that normally seal the end of the pen. These seem to fit tightly enough to prevent the other contents of my kit from turning yellow so are presumed to be airtight. I have only just assembled this kit 2 months ago so I havn't come to the 3 month replacement time. I am running a sort of experiment here. If they come out after 3 months with no noticeable degradation or coloration or weakening of the tube then I will consider this packaging safe. If you can find out the actual composition of this plastic let me know. So far everything seems sealed and stable. The internal diameter of the tube fits the iodine tablets accurately enough that they don't rattle around and if you cut the caps a little shorter than production length they will fit snugly without taking up too much room. On one of the caps I flattened the edge of the cap so I can grip it with my leatherman and pull it off. I suspect that the xacto blades would be able to cut that tube open well enough in an emergency but then I wouldn't be able to re-seal it. I remember biting these caps off back in highschool and being able to re-insert them....<br><br>I suspect that I will be able to open a close this adequately in the field.