Materials & Engineering

What it's made of, and why that costs more.

The steel: 304 food-grade. There are two grades in the bottle market and the difference matters more than the price gap suggests. 201 steel is cheaper — less nickel, more prone to pitting. Once the surface pits, it starts holding flavour. That's why a cheap bottle eventually tastes like a cheap bottle. 304 steel doesn't pit, doesn't rust, and doesn't take on the taste of anything. It costs roughly300 more per kilo. Every HydroBot uses it.

The vacuum: where bottles actually fail. A double-walled bottle is two steel shells with the air pumped out from between them. Heat needs something to travel through — with nothing there, it can't cross. That's why the outside stays at room temperature no matter what's inside. The seal on that vacuum is the hardest part to get right and the first thing to fail. When a bottle "stops working after a few months," this is almost always what happened. Ours are welded by hand and pressure-tested twice — once after welding, once after finishing.

The finish: powder coat, not paint. Paint sits on top of steel. The practical difference shows at the base, where every bottle takes its damage.

The tests.  Cold retention: filled with 1L water at 4°C and 200g ice at 09:00, ambient 43°C; at 03:00 the following day — 18 hours — water measured 6°C with ice still present. Hot retention: filled at 95°C at 21:00, ambient 22°C; at 09:00 measured 80°C. Drop test: 30 metres onto concrete, base-first, boot fitted. Leak test: filled, sealed, inverted and shaken 45 minutes.