While Thermos may be a well known and generic term for a flask, it’s just one of many brands. In fact, the best flasks come in all shapes and sizes and under many names. Our recommendations below have managed to master the art and science of the vacuum flask – that ingenious, insulated container that does the job of a portable kettle or fridge without the need of a plug socket.
Whether it’s a chunky “food flask”, sleek “vacuum bottle” or something in between, the job of a flask is to keep food and drink hot or cold without leaking, all day long. Some of the winners on our list can insulate for more than 24 hours, which is long enough to survive the toughest hike or most gruelling commute.
For this article, we’ve picked out several flasks that excel at insulation, leak-proofness, durability and, of course, value for money. Before you scroll on, take a look at our buying guide below for some helpful tips on buying the best flask.
How to choose the best vacuum flask for you
Flasks have come a long way and today’s best vacuum flasks are mini engineering marvels. Made from multiple layers of BPA-free and rust-proof stainless steel, these flasks should survive years of bumps and knocks, keeping you in hot cuppas and ice-cold drinks season after season.
They also win big on green points, doing away with the need to buy drinks in single-use cups. If your flask is big enough for lunch you can save on both money and plastic.
How much should I spend?
You can buy flasks for next to nothing but given how often you’re likely to use your flask, it’s worth spending a bit more for quality and durability.
You tend to get what you pay for when buying vacuum flasks. Of course, you can get flashy designer flasks but if you’re looking for quality alone you won’t have to spend more than about £25-£30. That may seem extravagant for a drinks container, but you’ll soon save much more on drinks and lunches.
What features should I look out for?
18/8-grade steel: Today’s best flasks are made from stainless steel that doesn’t secrete chemicals (they’re BPA-free, in other words) or weird flavours. The best of the best are made from 18/8-grade steel (aka 304-grade), whose high nickel content makes it rust-proof and extremely durable. It’s also non-magnetic, which may disappoint if you’d hoped to adorn your Thermos with fridge magnets.
Multi-wall insulation: Double-wall insulation creates a vacuumed layer, which is vital for keeping hot drinks hot and cold drinks cold. Some flasks include more layers for even better insulation. The 100% stainless steel construction of today’s flasks means there’s no risk of inner walls shattering when dropped.
Insulated cup: Good flasks also pay attention to the insulation of the detachable cup, if they have one. This is so your drink stays warm while you’re drinking it. Meanwhile, the outside stays cool, so you don’t risk burnt hands.
Capacity: Bigger capacity means more contents to enjoy. It also means more weight to carry, but only if you fill it to the brim. For best insulation, buy a flask that’s slightly bigger (but not heavier) than you need, and leave a couple of centimetres of air at the top. We’ve included capacity and weight info for all our flasks below.