Flasks are more 'smell prone' than 'stain prone' – none of the flasks we tested had any staining after cleaning, but some retained a faint coffee smell. Like many reusable water bottles, such as the Hydro Flask 24 oz Standard Mouth with Flex Straw Cap and the Iron Flask 25 oz Retro Water Bottle, this ThermoFlask drinkware is made of 18/8 food-grade stainless steel. It is free from harmful chemicals and toxins, so it is safe for you to drink from. This material also doesn’t rust, so you can expect it to last for a long time with proper care. None of the flasks leaked from the main body – however, some flasks can't be filled to their stated capacity without liquid coming out when you screw on the lid. Other useful design features to look for include a wide mouth, which makes for easier cleaning and filling (especially if you want to add ice cubes to your flask). In addition, many larger flasks incorporate ‘twist and pour’ spouts, so you can pour from the flask without having to completely remove the stopper. An integrated cup is also useful. Smaller flasks often feature lid designs that allow on-the-go swigging or one-handed operation. Like almost any decent bit of outdoor kit, a good vacuum flask should also be robust and durable. All the flasks we tested are made of high-quality 18/8 food-grade stainless steel that resists dents, dings and scratches. The trade-off with steel flasks is that they can be heavy, although modern designs are shaving weight all the time, and in some cases, they now weigh little more than a standard plastic drinks bottle.

Further, on the contrary, the Hydro Flask 24 oz Wide Mouth with Straw Lid is not suitable for hot liquids. The Wide Mouth with Straw Lid is not spillproof. This is where you get a win with ThermoFlask water bottles with straw lids, which are leakproof when appropriately closed.Button-operated lids are more efficient to use than twist-and-pour stoppers – we found the button-operated lids to be more secure than the twist-and-pour stoppers.

We’ve reviewed a selection of the best thermos flasks, ranging in size from 470ml to a whopping 64oz (1.8 litres). Bigger flasks usually retain heat better than smaller flasks, but are typically bulkier and heavier. We’ve compared their performance with our own temperature test. What Is The Best Thermos Flask? Capacity: 592ml/20oz / Temperature test: 0 hrs 90°c, 90 mins 81.7°c, 4 hrs 72.4°c, 6 hrs 65.1°c, 8 hrs 59.9°c, 24 hrs 36.2°c / Double wall vacuum stainless steel construction / Screw in stopper with leakproof flip top lid / Powder coat finish / BPA-free and phthalate-free / Dishwasher safe (hand wash recommended). BUY NOW: EARTHWELL.COMKey attributes: Leakproof, practical design enables one-handed drinking, wide mouth for easy filling and cleaning For the sake of this particular comparison between a ThermoFlask bottle and a Hydro Flask bottle, we will refer to the ThermoFlask 24oz Bottle with Chug Lid and Straw Lid, and the Hydro Flask 24 oz Standard Mouth. As the name implies, this water bottle has two lids— the Chug Lid and the Straw Lid. You can drink the way you want with these lids, even with a one-hand operation.