When sourcing waterproof luggage, prioritize materials like Polycarbonate (PC) or Polypropylene (PP) for hard-shell cases, as they are inherently non-porous. For soft-shell options, ensure the fabric is TPU-coated nylon or polyester with a high denier count (e.g., 840D or 1680D). Crucially, look for seamless high-frequency welding technology rather than traditional stitching, and verify the use of water-repellent zippers (e.g., YKK AquaGuard) or a gasket-sealed aluminum frame to prevent leakage through closure points.