Sealock manufactures waterproof duffel bags for OEM and wholesale buyers at factories in China and Vietnam, and the process rests on a constraint most buyers never hear about. High-frequency welding — the technology that makes a bag genuinely waterproof — works against a flat base plate and is therefore best at producing flat seams. A duffel is a three-dimensional vessel. Reconciling those two facts is what duffel manufacturing actually is, and it explains the tooling costs, the lead times, and why some designs quote easily while others do not.