Reviews You Can Rely On

Thermos Guardian Stainless Hydration Review

A vacuum insulated bottle with a lackluster feature set
Thermos Guardian Stainless Hydration
Credit: Amazon
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Price:  $25 List | $29.20 at Amazon
Pros:  Affordable, easy to clean
Cons:  Leaks, flip-cap is challenging to operate, lacks durability
Manufacturer:   Thermos
By Jane Jackson ⋅ Senior Review Editor  ⋅  May 26, 2021
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  • Ease of Use - 40% 5.0
  • Durability - 25% 4.0
  • Weight - 20% 4.0
  • Taste - 15% 6.0

Our Verdict

The Thermos Guardian Stainless Hydration is an affordable option for an insulated stainless steel bottle. It is easy to clean and resists lingering flavors. That said, we were not that impressed with the overall feature set on the Guardian. The flip cap design didn't operate smoothly and the carrying handle was weirdly shaped and not ergonomic. In summary, we were underwhelmed by the performance of this bottle in our side-by-side testing.

Our Analysis and Test Results

The flip cap is becoming more and more prevalent in water bottle design across the board. Stainless steel, plastic, and glass bottles are now often coming with a one-handed button-operated lid. The Thermos Guardian is one such bottle, but unfortunately our least favorite iteration of this design we've tested. The Guardian was not easy to operate and its carrying handle felt bulky and poorly shaped. It did insulate fairly well and didn't impart flavors too much.

Performance Comparison

Thermos Guardian Stainless Hydration water bottle - a flip-cap, push-button bottle that isn't as effective as many of...
A flip-cap, push-button bottle that isn't as effective as many of its competitors.
Credit: Jane Jackson

Ease of Use

This metic is really where the Thermos Guardian falls short. The lid has a push button, a locking mechanism, and a carrying handle, but all of these features felt like they were made from cheap materials that didn't work very well. The lock worked but felt gimmicky. The push-button was sticky and often required a second push to actually open. Finally, the carrying handle doesn't fold flush against the bottle, so it sticks out at a 90-degree angle when not in use, which bothered our testers. On the plus side, it is easy to fill and clean, as its wide mouth accommodates a bottle brush easily. The lid, though complex and clunky, also cleans fairly easily due to its wide spout.

Thermos Guardian Stainless Hydration water bottle - the guardian is great for hot weather - it is insulated and you can...
The Guardian is great for hot weather - it is insulated and you can keep track of your water intake through the regulator on the top of the bottle.
Credit: Jane Jackson


Overall, this stainless steel option did well in our durability tests. When dropped, the bottle got a few small scuffs and a small indent on the bottom, but beyond that was unscathed. This is typical for a stainless steel, insulated bottle, but we were pleased nonetheless.

Thermos Guardian Stainless Hydration water bottle - the locking mechanism and the flip cap in general on this bottle...
The locking mechanism and the flip cap in general on this bottle lacked durability.
Credit: Jane E Jackson

When it came to our leak test, though, the Thermos Guardian was a little less impressive. When shaken, even with only water inside, the bottle leaked a few drops out of the flip cap. When left resting on its side filled with colored water, a few drops leaked out onto the paper towel after a few hours. Again, this reaffirmed our lack of confidence in the overall lid design on this one.


In comparison to its stainless steel peers, the Thermos Guardian is impressive when it comes to weight. Though its capacity is only 24 ounces, the bottle weighs in at 12.7 ounces, giving it a weight-to-volume ratio of 0.53 ounces. This is on the lighter end of the spectrum in the world of vacuum-insulated bottles.

Thermos Guardian Stainless Hydration water bottle - the guardian outperformed its stainless steel competitors on the...
The Guardian outperformed its stainless steel competitors on the scale.
Credit: Jane Jackson


When we conducted our taste test on the Guardian we were impressed by its easy-to-clean design and its ability to shed flavors. If this bottle has a strong suit, this testing metric would certainly be it. After filling it with drink mix and then washing it with a bottle brush and a tiny bit of soapy water, the Guardian was more or less returned to its original state. Additionally, there were no plastic-y flavors when we took it out of the box initially, adding to its high score in this metric.

Thermos Guardian Stainless Hydration water bottle - even with its complex lid, the guardian impressed us with its...
Even with its complex lid, the Guardian impressed us with its ability to shed flavors after a quick rinse.
Credit: Jane Jackson


This is a very affordable bottle, especially compared to its vacuum-insulated, stainless steel counterparts. The Guardian is on the cheaper side of most of the bottles we tested and it shows. We hate to say it, but this bottle doesn't seem like it was built to last. The flip-cap started to get sticky after only a few days of use and the locking mechanism was prone to get stuck as well.

Thermos Guardian Stainless Hydration water bottle - while this bottle isn't a failure, it's also far from our favorite...
While this bottle isn't a failure, it's also far from our favorite bottle to use in nearly any situation.
Credit: Jane Jackson


Though it's affordable, the Thermos Guardian was not our favorite bottle in the line-up. Its feature set left a lot to be desired — the buttons were clunky and the carrying handle was ill-sized and bulky. It is easy to drink from the spout, but the button to open the flip cap didn't work very well. We think most folks will be better served looking for a different bottle with fewer gimmicks and more simple functionality.

Jane Jackson
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