This simple, inexpensive, reusable cap for open caulking tubes has saved innumerable partially used tubes of adhesive or caulk from being thrown out and has paid for itself many times over. This cap forms an airtight seal around the entire tip of the caulking tube and the long center spike creates and keeps open a channel for the material to flow out. It has never failed over several years to preserve all sorts of materials. I have often been left with a partial tube of material after some project or other and this cap has always allowed me to pick up that tube, even after many months and to continue to use the contents.
Like all of us, I had tried wrapping the tip in cellophane, shoved a nail down the tip or tried some other solution. None was successful. The other advantage is that the center spike is slender enough to fit down a tip which you have cut with a very fine opening. There is no distortion of the tip and no need to recut it. All in all an elegant solution to a common annoyance and a real money saver.