This is a cotton ball inside a straw to keep it dry.
Step 1: Melting the First End
You can put anything inside a star to keep it dry, but if it is a gelatin like substance keep both ends open until it is full. Put the straw on a pair of pliers with only about 0.9mm left sticking out. Then burn it with a lighter
Step 2: Filling Time!
If you are going to put a cotton ball inside, you should tear it into small pieces first, and then stuff it inside the straw with a skewer.
Step 3: Done
Now you have a waterproofed what ever!