Iron Flask vs Thermoflask

Imagine the following situation: you’re hiking on a hot summer day and you’re starting to feel thirsty. Fortunately, that’s a problem you can solve quite easily – you just need to grab your hiking water bottle and take a few sips. But alas! The water you were carrying in your backpack is now lukewarm and tastes just horrible.

This is precisely why more and more outdoor enthusiasts are deciding to go with stainless steel water bottles instead of their plastic counterparts. Not only can a bottle of this type maintain the temperature of your drink for a long time, but it’s also far more durable and eco-friendly.

If your search for the best stainless steel bottle brand has narrowed down to Iron Flask vs Thermoflask, you’re in the right place. Join me in taking an in-depth look at the two most popular products made by these renowned drinkware companies:

Iron Flask vs Thermoflask – Product Overview

Iron FlaskThermoflask
Weight1.58 lb1.80 lb
Volume40 oz40 oz
PriceNo products found.No products found.
MaterialStainless SteelStainless Steel
ImageNo products found.No products found.
No products found.No products found.

Iron Flask 40 oz 3-Lids Bottle

Purple Iron Flask


  • Volume: 40 oz
  • Weight: 1.58 lbs
  • Material: Stainless steel
  • Available colors: 25

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It’s quite easy to see why is this particular Iron Flask bottle one of the brand’s best-selling products. Available in a myriad of eye-catching colors (as well as several additional sizes), the 40 oz 3-Lids bottle excels in every department – user-friendliness, durability, temperature regulation, and others.

As its name suggests, the model comes accompanied by three different lids, which makes it extremely versatile and suitable for use in a variety of scenarios. The 18/8 stainless steel construction, on the other hand, ensures genuine durability, while the double-walled vacuum insulation effortlessly maintains the temperature of hot and cold drinks. It is a great alternative to Yeti as well as a great alternative to Hydro Flask.


  • 3 practical lids
  • A durable, user-friendly design
  • Available in 25 colors


  • A sharp handle on the flip lid

Thermoflask 40 oz 2-Lid Bottle

Blue Thermoflask


  • Volume: 40 oz
  • Weight: 1.80 lbs
  • Material: Stainless steel
  • Available colors: 5

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Just like in the case of Iron Flask and its 3-Lids model, which I have described above, this particular bottle is one of Thermoflask’s most popular products. And that’s not only due to the fact that it’s very affordable – this bottle is also very practical, functional, and, of course, long-lasting.

Besides durable stainless steel, the model also sports some BPA-free plastic elements in its construction. It has a wide mouth, which makes cleaning it and filling it with ice as easy as it gets. Finally, it doesn’t hold onto flavors and has a sweat-free exterior. What more could one want?


  • Sweat-free exterior
  • Doesn’t hold onto flavors
  • Easy to clean & fill with ice


  • Lid issues (more on this down below)

Iron Flask vs Thermoflask – The Face-Off

Women sharing a water bottle

Ease of Use

Both of these bottles feature a user-friendly design – there’s no doubt about that. User-friendliness is certainly an important factor, as nobody wants to use a stainless steel bottle that’s complicated to drink from. However, even though these models do sport a practical design, each of them has a few lid-related issues.

For example, the flip lid of the Iron Flask bottle featured in this comparison has a somewhat sharp underside. I would definitely like this part to be a bit smoother – it’s bound to leave painful marks on the hands of people with sensitive skin.

The straw lid of the Thermoflask bottle, on the other hand, will require you to apply a bit of pressure to it in order to achieve adequate water flow. This is because it doesn’t lock into place when it’s in the drinking position. While this certainly isn’t a dealbreaker, it’s definitely annoying and may make some folks regret buying this bottle.

Another issue I found with Thermoflask’s straw lid is that the seal where the straw connects to the top isn’t tight and “proper”, so to say. Whenever I tried to drink with it, I would also intake some air along with water. Keep in mind that this is an affordable stainless steel model and that you can’t really expect a flawless design.

Construction Quality

In terms of construction quality, these bottles are quite similar. None of them are as durable as, say, Yeti’s stainless steel bottles, but they’re still exceptionally well-made and should last you for years as long as you take good care of them.

Unfortunately, however, accidental drops are often unavoidable, so I decided to see how each of these bottles fares in a drop test. Upon dropping the Iron Flask model from a height of about 5 feet, I noticed that the model ended up with just one minor indentation. After all, this bottle was made out of premium-grade 18/8 stainless steel.

The results were pretty much the same for the Thermoflask bottle. I dropped it onto a concrete surface from the same height and there was just one tiny dent and some scratches. One important thing to mention here is that this model has a genuinely sweat-free exterior and won’t succumb to corrosion anytime soon.

So, in summary, you can’t really go wrong with either of these models if you want your bottle to be durable. I think that the Iron Flask bottle is a slightly better choice in this regard, although none of these products are as long-lasting as the ones made by Yeti (or as expensive, for that matter).


Woman holds a white bottle

The next important topic to talk about is insulation. After all, insulation is the main selling point of these products – unlike their plastic counterparts, insulated stainless steel bottles can maintain the temperature of both cold and hot drinks for hours on end, which can come in very handy during long summertime/wintertime hikes.

Iron Flask claims that their 3-Lid bottle, which is featured in this comparison, can keep a cold drink cold for about 24 hours. I can confirm that this is true – while there was no ice left in the bottle after one whole day, the water in it was still relatively cold. They also claim that the model can keep a hot drink hot for 12 hours, but in reality, it cannot do so for more than 8 hours.

The same can be said for its rival. The Thermoflask 40 oz 2-Lid bottle can also maintain the temperature of cold drinks for one whole day, which is quite impressive for such an inexpensive piece of drinkware. Unfortunately, however, it can’t keep coffee or tea hot for more than 6 to 8 hours, even though Thermoflask claims that it can do so for about 12 hours.

If you’re looking for a stainless steel bottle that will keep your water cold during sweaty summertime walks, you won’t make a mistake by going with either of these models. However, if you want something that will be just as good when it comes to keeping hot drinks hot, you’ll have to look elsewhere.


If there’s one good reason why an outdoor enthusiast would choose a plastic water bottle over a stainless steel one, then it’s the taste. Namely, the first bottles made out of this material were quite notorious for their proclivity to give an awful metallic taste to the drinks contained in them. This is one of the reasons why some people still refuse to get themselves a bottle of this type.

Fortunately, the newer models – particularly the ones made by renowned brands – do not have this problem anymore. Neither of the two bottles featured in this comparison affects the flavor of drinks in any way.

What is more, neither the Iron Flask nor the Thermoflask model has any issues with flavor retention. The fact that both bottles come with multiple lids really helps here – if one of the lids does manage to somehow hold onto a particular flavor, you can just swap it for another one.

Ease of Cleaning

Young couple hiking

The flavor retainment issue I mentioned above is not something you need to worry about if you’re someone who regularly cleans their water bottles. And since both of the bottles featured in this article have wide mouths, you’ll have no trouble with cleaning either one of them.

One particularly important thing to mention here is that you should never wash either of these flasks in your dishwasher. While this is something that can be done, both manufacturers advise hand-washing only. For the best results, use soapy water and a good bottle brush.


The Iron Flask bottle described in this comparison costs just a few dollars more than its rival. Is this higher price justified? In my opinion, it is – the model comes with three instead of two lids and is, therefore, more versatile than the Thermoflask bottle.

The Thermoflask model is still a worthwhile purchase, though. If you’re shopping for a new stainless steel bottle and want to save as much money as possible, you won’t make a mistake by going with this product – it’s durable, practical, and it keeps water cold for hours on end. If you would like to check out more affordable water bottles, read this Hydro Cell vs Iron Flask comparison as well.

Wrapping It Up…

Hiker drinks out of a big bottle

Both of these stainless steel bottles are in the same price category and have the same durability and performance. In other words, you can’t go really wrong by purchasing either one of them.

If I had to choose a winner, though, that would probably be the Iron Flask 40 oz 3-Lid bottle. While it does cost more than its rival, it’s available in more colors, it weighs less, and it comes with three instead of two lids, which turns into a more versatile option. You may also want to check out our Iron Flask vs Simple Modern  and our Iron Flask vs Takeya comparison.

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