All salt is sodium chloride (NaCl) but in the kitchen, all salt is not the same. In the video above from America's Test Kitchen, Jack Bishop explains the different types of salt you need in your kitchen while this article compares Diamond Crystal Kosher Salt to Morton Kosher Salt and why they prefer the former:
The process used to make Diamond Crystal salt differs from Morton's process in a few important ways. Diamond Crystal is the only company in the United States to use the Alberger process, a technique developed in the 1880s that heats and agitates the extracted brine in a series of open containers. The combination of slow heating and agitation causes hollow kosher salt crystals to form on the surface of the brine. (For more information, see this graphic from Cargill, which owns Diamond Crystal.) As larger crystals form, smaller crystals also form and stick to the larger crystals, resulting in a mix of shapes and sizes. Unlike the grains of Morton kosher salt, the larger grains of Diamond Crystal kosher salt are not flattened or flaked before packaging.