Kids will adore the array of colors and character themes the Funtainer comes in. More importantly, a wide brim makes eating less challenging for little ones getting the hang of using utensils, and the stay-cool exterior won't harm their hands. Best of all, it's lightweight and compact enough for little hands to open and carry in their lunch box. Best for big meals – SHO’s Ultimate Food Flask is not the biggest flask out there, but it is bigger than most. 2 sizes are available for the Ultimate, both of which are bigger than comparable flasks. The smaller is 600ml, which beats out other similarly sized flasks which are usually around 500ml, and the 800ml compares with others usually around 700ml. So unquestionably, if you’ve got a big appetite (or are carrying food for two) then the Ultimate should be your flask of choice. An honourable mention does go out to Pioneer’s 1000ml food flask, however.

Thermos King states this can keep liquids hot for nine hours and cold for up to 14 hours, so we put that claim to the test in a home kitchen. Our reviewer filled all 16 ounces with freshly made mac and cheese and opened the thermos every hour to see if the temperature remained consistent. It wasn't until the ninth hour that the temperature dipped. Additionally, it excelled at keeping water ice-cold, with our tester still observing ice cubes after 14 hours in the thermos. 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.High-quality thermal flasks can keep food and beverages warm for as long as a full 24 hours. More economical brands will typically retain the original temperature of contents for four to six hours. The size of a thermos largely depends on what you want to use it for. Most thermoses for adults tend to be around 16 ounces, and ones for children are a little smaller. The food will cool down faster if there is excess air in the thermos, so if you want your food to stay hot for several hours, you'll want to use the best size thermos for the amount of food you're putting in it. If you just want the option for a small soup bowl at lunch, you can go with 10 ounces or smaller. If you want to carry a hearty meal in your flask, 16 ounces is likely the better fit. It’s 100% leak proof – no matter how hard we tried, we couldn’t get any liquid to escape and the automatic opening trigger means you can drink from it one-handed with ease. Finally, there’s an additional loop handle on top so it can easily be attached to bags or simply carried this way. All in all, this is brilliantly stylish and robust

A Thermos King will last years but it’s not officially dishwasher-safe, and you’re not even meant to submerge it in water (if you do, you kill the manufacturer’s 50-year guarantee). Inquisitive users report that it does survive the dishwasher intact, albeit with peeling colour. The amount of food you can get into your flask should be one of the main considerations you make when looking for the right food flask. Nobody knows your appetite and eating habits better than you do, so take a close look at the volumes of the flasks you’re considering and weigh that up against how much you’d be looking to carry. After all, it defeats the point somewhat if you can only fit half a lunch portion in what you’ve bought, or on the other end of the spectrum, buy one that’s too big and realise you’ve wasted money on flask volume you just won’t fill. Also bear in mind how many people you’re feeding – one large flask might feed two, if you’re going on a trip somewhere and are trying to economise on how much to take with you. Lid 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. Whatever it is you need from a flask, our buying guide is here to help you make a bit more sense of what you need in terms of the most essential criteria – after reading this, you should be absolutely sure which food flask is right for you. Capacity

The verdict: Insulated flasks

Thanks to an uber-tight seal, the Thermos King is touted as having maximum temperature retention for hot and cold food. That's thanks to the insulation from two walls of stainless steel. Another significant benefit is that the lid is designed to be used as a bowl in tandem with the included standard-sized stainless steel folding spoon. Of course, one of the main reasons to buy a flask is to keep hot food hot. As such, heat retention is another of the most important factors to consider before buying. This heat retention time can vary hugely between around 4 hours, up to 12 hours and potentially even longer than that. This means that you have to factor in how, where and when you intend to use your flask. For single portions, a few hours is probably fine, but on longer expeditions with multiple meals, you’re naturally going to need one that’ll hold onto that heat for longer. UP TO 6 HOURS COLD: Keep your cold food crisp and fresh for up to 6 hours in 500ml and 5 hours in 300ml. Perfect for sunny days out at the park or on the beach. No need for a separate cool bag, just grab your pot and go!