Most buyers start with a price sheet and end up with a quality problem six months later. The factories that cause trouble are rarely the expensive ones — they are the ones nobody visited.
1. Ask which processes happen on site
Tube cutting, metal forming, vacuum brazing, polishing and coating are the steps that decide whether a bottle holds vacuum for years or fails in a warehouse. If a supplier outsources vacuum brazing to a third party, they cannot control that step either.
2. Look at how they handle the lid, not the body
Bodies are commodity. Leaks almost always originate in the lid: gasket durometer, thread pitch, drinking-spout tolerance. Ask for the cycle-test data behind the lid you are buying.
3. Test the sample like a customer would
Drop it. Fill it with hot water and hold it. Leave it in a hot car. Put it in a bag upside-down. A supplier who welcomes that is a supplier worth keeping.
4. Check the paperwork before the discount
FDA, LFGB and Prop 65 test reports should be issued against your actual product, not a similar model. A report with a different model number on it protects nobody.
5. Talk about the second order
The real test is whether order two matches order one. Ask how colour is matched, how print screens are stored, and how long a specific Pantone reference stays on file.
