Lamellar was by far the most common form of leather armor. This was the most ubiquitous and arguably the most effective form of leather armor used historically. Fairly flexible and relatively good protection. Plus it floats.
The first row represents the protective quality of the Helmet or the lamellar brigandine over the gambeson, the second row represents the protective quality of the gambeson alone. See Armor Table Key, Layered armors for more about how this works.
|Panoply, Cuir Boulli Lamellar