Glossy promises of a perfect cuppa from your high quality, thermos cup might tempt you to buy one, but not all thermal flasks are created equal.

To enjoy hot drinks at their best for as long as possible, there are a few things you should look out for when choosing a thermal flask. And the good news is that once you have the right type of flask, it will take care of itself – no need to put much effort into maintenance.

1. Purity matters: The easiest way to spoil a good cup of tea or coffee is by using a dirty or badly scratched flask. Tea and coffee contain tannic acid and caffeine so that they can stain the inside surface of the flask – and it becomes harder for you to get rid of the stains. These substances are water-insoluble, so they can only be removed by scrubbing, which damages the surface even further. Any other residue left behind in your flask might also spoil your drink.

2. Go stainless steel: Your best bet is a stainless steel thermal flask, which offers excellent heat retention (and doesn’t affect the taste). The double-walled body construction acts as an insulating layer between the inside and outside, trapping heat inside for longer before it escapes into the surrounding air.

3. A wide mouth makes cleaning easier: It might seem like common sense to look out for a slimline design when choosing a flask, but unless you want to spend more time cleaning it than drinking from it, go for the opposite and choose a wide mouth flask.

4. High-quality screw: Once you’ve found a flask with all of these features, here’s one last thing to look out for – the flask’s cap. The best caps have a screw thread that fits just as well after five years as when you first bought it! A poorly made cap will damage the stopper over time and affect how well your drink stays warm/cold – so check what type of closure system your chosen flask has before purchasing it.

5. Use correctly: Finally, make sure you properly use your new thermal flask. Thermal flasks work on physics principles and can’t create something (heat) out of nothing (the power supply). If your drink is already cold, to begin with, it will never get hot enough for you to enjoy. Likewise, if the flask wasn’t pre-chilled before adding the hot liquid, you’ll have lukewarm tea/coffee when you come back from a long day at work.

So make sure your flask is always filled with boiling water or freshly boiled drinks and add in any milk/sugar while the liquid is still warm – this will keep it cooler for longer.