This is called a J/J for a reason - modern fabric technology has allowed us to create a garment that can neither be defined as a long sleeve jersey or a jacket. In the past a long sleeve jersey would have a fairly small operational temperature range, often needing layering underneath or over the top to handle fluctuating conditions. A jacket has a different problem, more often than not it would end up being too hot under effort. The J/J can be considered both a jersey and a jacket, being able to handle a large temperature range.
The reason for this is the material used, it is a 3ply fabric, meaning it is constructed by bonding three layers of differing fabrics together with a foam core. It is this foam core which gives it not only the performance advantage but the unique look, it bears a striking resemblance to a 1980’s diving jacket, or similarly a sci-fi biker jacket, there is nothing else like it out there. The performance advantage is due to the fact the foam wicks the sweat away from the body while also providing wind protection without compromising the breathability, this is why it can handle such varying conditions.
The piping around all the seams is there for performance reasons as it prevents the three fabrics separating at the edges where it has been cut, although there were purely practical reasons for this it has also added to the overall look of the J/J.
The overall cut of the J/J is more like a jersey than a jacket, allowing it to be more fitted than a jacket normally would be, there are three rear pockets and also a vertical chest pocket with a zipper closure. The zip for this pocket and the main zip are quite chunky yet lightweight, it made sense to have a zip that had a bit more presence than normal in order to fit with the aesthetic. The neck line is slightly higher than a jersey, more like a jacket, everything about this garment is difficult to define apart the performance, which has created its own definition – the Jersey/Jacket.