The #2 stopper was chosen for this design because it is easily purchased online or from your local home brewing store. I have used a natural rubber stopper for my product; however there is a similar silicone product. I continue to debate the qualities of each material. I like the idea of using natural rubber in a product that is close to my food; yet, it will degrade quicker than the silicone stopper.
The solid stopper can be used to remove the air lock and seal the container with the fermenting lid. It is intended as a stop-gap measure, only untill a regular mason jar lid can be installed. We included it because, hey, I know what it is like to be rushed.