Looking for a cost-effective way to enjoy hot or cold drinks away from home? Why not invest in a new thermal flask. While Thermos might be the dominant brand of vacuum flask, there are many excellent models available at great prices that are worth considering.

Modern insulated flasks can maintain the temperature of its contents for most of a day and give you the convenience of enjoying a beverage on the road, at a picnic, or in the office. A flask can be carried while hiking or when traveling by train or car, and can reduce personal expenses: filling a flask with tea, coffee, soup or a cold drink at home saves money that would otherwise be spent in cafés.

What to look for in a Thermos or vacuum flask

Flasks vary in price by brand, capacity, material-of-manufacture and design. Typical capacities run between 10 to 30 fl oz, or enough for four typical cups. Cheaper thermal flasks are manufactured from plastic but more durable, better quality flasks are made of metal, usually stainless steel. Some specialist thermal flasks (especially those used in laboratories) have non-reactive glass liners. Design has an impact on price and efficiency: insulation is achieved either by double-walling the flask (with a narrow air gap between the layers) or by vacuum-sealing a gap between the flask’s exterior casing and a liner. The vacuum provides better insulation but this design is usually more expensive. Additionally, it is important to have an insulated plug in the top of the flask; we like screwed plugs with a washer for a good seal and best heat retention.

Stainless steel-lined flasks tend to steal heat from warm liquids when they’re being filled because the metal is colder than the liquid. One way to obviate this is to fill the flask with boiling water, then discard the water and refill the flask with the beverage or soup that you intend to carry with you.

To many people ‘Thermos’ is eponymous with thermal flask, and we’ve included two excellent representatives of that brand in our list, but don’t disregard other manufacturers immediately as there are some real gems out there.

Best Insulated Flasks

Pioneer Stainless Steel Flask 17 fl oz – Best budget flask

Pioneer flasks are available in five sizes between 0.3L and 1.5L and in eight different colors. The 500ml (17 fl oz) flask is a convenient ‘rucksack’-size for two large cups of tea or coffee. The flask is manufactured with a stainless steel liner and is vacuum-insulated. It claims to maintain hot drinks for 8 hours and cold drinks for up to 24 hours. The screw-stopper has a push-in pourer that enables you to pour a drink without removing the stopper. The flask is capped with an insulated cover that doubles as a cup. The Pioneer flask is fairly priced and is well worth considering if you do not need special features or performance.

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Azuma 1L Bullet Thermal Flask – Best affordable large flask

The Azuma Bullet is an all-stainless-steel, double-wall insulated flask. The screw-in stopper has a flip opening that permits both easy filling and convenient pouring without exposing the contents to external temperatures. The flask and stopper are protected by a top-cover that can also be used as a cup. The flask is 12 inches high with a diameter of 3.3 inches. Heat retention may not be as efficient as in more expensive flasks and the ‘build’ is not heavy-duty but the Azuma Bullet is an economy-priced flask that can nevertheless ‘do the job’ in most circumstances. This flask is also offered in smaller 350mL, 500mL and 750mL sizes.

Thermos ThermoCafé Flask 1L – Best cheap Thermos

The ThermoCafé is offered in three different sizes but we like the 1.0 L (34 fl oz) for its larger capacity at an everyday price. This is a vacuum-insulated flask with a stainless steel exterior and liner. The top cover can serve as a cup and, beneath, there is a twist and pour stopper. The manufacturer advertises that it will keep liquids hot for up to 8 hours, or cold for 24 hours. The design is tall and slender (12 inches high with a base diameter of 3.5 inches) and the finish is brushed metal. The ThermoCafé is a deserved best-seller and an excellent buy for anyone seeking a good flask at a sensible price.

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Rhino 500 mL Vacuum Flask – Best sports flask

The Rhino flask is designed for hiking and camping but will be equally suitable for office use. It is vacuum-insulated with a stainless steel casing and inner liner. Unusually, the outside of the liner has a thin copper-coating that helps reduce heat conduction into the insulating vacuum layer. Rhino claims its flask will keep drinks hot for 6-12 hours, or iced drinks cold for up to a full day. Rhino’s design features a wide, screw-in insulated ‘sports stopper’ that incorporates a flip-open cap for easy pouring. The wide opening makes it easy to place ice cubes in the flask while the smaller cap-opening limits heat loss when pouring. The flask has a slender profile, measuring 10 inches from top to bottom, and the casing is finished in a matt black powder-coating. This Rhino flask is a sturdy piece, at a very reasonable price, that should give long service.

Thermos King Food Flask 24 fl oz – Best for chunky soups

The Thermos King Flask is chosen for its stubby design and wide mouth that makes it suitable for carrying ‘chunky’ soups or stews. The mouth permits easy filling and cleaning, and the vacuum insulation will keep liquids hot for 14 hours or cold for 24 hours. It is constructed from stainless steel throughout and the screw-down, insulated lid can be used as an eating bowl. Overall dimensions are 3.7 x 3.7 x 7.2 inches. The King flask is a durable offering, available in a variety of colors, and is an excellent choice for hot, winter lunches.

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Stanley Classic Vacuum Bottle – Best luxury flask

Stanley Classic Stainless Steel Vacuum FlaskStanley’s Classic flask is offered in ‘hammertone’ green or navy and five sizes (1.1qt, 1.4qt, 16oz, 25oz, 2qt). With the insulated cup-top in place, the 1.1qt capacity flask is 14 inches tall and the base has a 4 inch diameter. The flask is constructed of stainless steel and is vacuum-insulated. The manufacturer claims it will maintain drinks hot or cold for at least 24 hours. We like the useful, side-mounted carrying strap and the flask’s rugged feel and finish. Reviewers confirm that the Stanley Classic Bottle offers excellent durability and thermal performance.

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