304 stainless steel is an iron alloy containing roughly 18% chromium and 8% nickel — a composition refined through a controlled smelting process in which raw materials are melted in an electric arc furnace, refined to remove impurities, and then rolled or drawn into finished form. The chromium content is the functional core: it reacts with oxygen to form a passive oxide layer on the surface, invisible and self-repairing, which is what makes the material genuinely corrosion-resistant rather than merely treated to appear so. The nickel addition stabilises the alloy's crystalline structure, improving formability and adding resistance to both acidic and alkaline environments. Against lower grades — 201, 202, and unspecified "food grade" claims common in cheaper drinkware — 304 holds its integrity across a far wider range of temperatures, cleaning agents, and contents.