At first glance the very idea of a zipper that unzips and zips up by itself seems somewhat ridiculous. After all, these contraptions are mostly used on pieces of clothing and gear where handling a …
While I knew your answer, I just went through a similar thing with a Costco jacket. It’s a winter jacket with a false fleece liner. As in, there’s a 2" strip inside the jacket, just behind the main zipper, that just zips up. While it can offer an extra inch of belly room after too much hibachi, the main benefit seems to be that it starts about 3" higher than the exterior zipper. It’s pretty good for driving in that mode.
While I knew your answer, I just went through a similar thing with a Costco jacket. It’s a winter jacket with a false fleece liner. As in, there’s a 2" strip inside the jacket, just behind the main zipper, that just zips up. While it can offer an extra inch of belly room after too much hibachi, the main benefit seems to be that it starts about 3" higher than the exterior zipper. It’s pretty good for driving in that mode.