Cups

Single-wall weighs less and costs half as much, but it sweats on the outside and cold water warms up within an hour. Vacuum double-wall doesn't condensate and holds the temperature for hours. For the office, single-wall does the job; for people on the move, double-wall is the one that actually gets used.

A vacuum double-wall bottle keeps things cold for eight to ten hours and hot for five to six. The difference lies in the vacuum between the walls, not the price: we ask for the technical sheet with the real retention hours and compare it with what the catalogue promises.

It depends on the technique. On steel, laser engraving marks the metal itself and never wears off. Colour printing holds up well if it's oven-fired; printing that only has a varnish coat gets scratched in the dishwasher. On ceramic, fired marking is the only kind that survives daily use in an office.

18/8 stainless steel, which is food-grade and leaves no metallic taste; a silicone seal, which doesn't dry out or pick up odours the way rubber does; and a lid free of bisphenol-A plastics.

The lid, almost never the body. We check that the thread has a long pitch, that the seal is silicone, and that the lid can be taken apart for cleaning. If it has a straw or spout, we check that spare parts are available.