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Hydro Flask 21 oz Standard Mouth

rated 4.0 of 5 stars
photo: Hydro Flask 21 oz Standard Mouth water bottle

I bought this bottle, based on rave reviews and positive reports from others on social media...purchased for use primarily for taking hot coffee out on early morning canoe trips. It is a very nice bottle, but I have found it does much better at keeping beverages cold, than it does at maintaining hot beverages.


  • Double wall insulation
  • Easy to grasp
  • Nice color seelction


  • Does not keep hot beverages at temperature as well as advertised.


I bought this particular size and shape of the Hydro Flask line, based on the description on the REI site. I often head out at 0500 for a few hours of canoeing, and it is nice to have hot coffee along for the ride. Other insulated mugs I have used have not kept coffee hot for more than an hour or so.

On the REI site, it clearly stated " keeps the contents hot for 12 hours and cold for 24 hours". Other models only claimed 6 hours of "hot-keeping," so this seemed the best bet. 

When the bottle arrived, I liked the nice green color I had chosen, to match my canoe...but I noted that the cardboard sleeve on the bottle said that it kept beverages hot for 6 hours. Well, I have found that even 6 hours is a stretch. Loading the bottle with coffee far too hot to drink, it still only keeps the beverage hot for 2 or 3 hours. After that, it is just lukewarm. REI acknowledged that their description was incorrect, and have since changed it on website.

So for hot beverages, it is just an adequate thermos type bottle. It is easy to grasp, with a nice outer finish, and the cap is easy to use.

The bottle will keep cold beverages for 24 hours; I have put in iced coffee, with lots of ice, and 24 hours later, the cubes were still there. That is quite good, and it is nice to be able to bring cold bevies along for a longer day paddle.


I will continue to use this bottle, at least 4-5 times per week, but primarily for short term outings with hot beverages, and for longer trips, to keep drinks cold. I cannot really recommend it over any other insulated bottle for hot beverages, but it is pretty cool at keeping drinks cold for long periods of time. For cold beverages, 5 stars...for hot, maybe 2 or 3!

Source: bought it new
Price Paid: $28

HYDRO FLASK Narrow Mouth Water Bottle, 21 oz.


  • Insulates well
  • Fits in cupholder


  • Difficult to clean if used with other liquids

This is a doubled walled stainless steel with a vacuum between the two walls so it insulates really well. It has the standard narrow mouth and cap. Even though I had the other two Hydro Flask bottles, my wife talked me into getting this one too, as it was on sale.

It turns out I like it a lot more than I would have thought. My main concern was that the narrow mouth would make it too difficult to put ice in it, but I find that I can squeeze a few cubes in, and then because it is so well insulated, it stays cold a long time. In fact, that prevents me from putting too much ice in it. 

The bottle is a little sleeker, so it is easier to carry, and it fits in cupholders. It is really nice to be able to have ice water on a hot day. I don’t use this one for adult beverages, or anything other than water, since I am concerned that the narrow mouth will make it difficult to clean. It is small enough to fit in some jacket pockets. The double wall construction does add some weight, but it is certainly worth it for the insulation.

Resting at home:


With the 18 oz wide mouth and the 40 oz wide mouth, and a Nalgene for comparison:


Source: bought it new
Price Paid: $22

Should be six stars.


  • Maintains temp for at least 12 hours
  • Durable

I bought two of these, one for my wife and one for me. Unfortunately my daughter took one so I sort of missed out. She would fill her bottle with ice water before school and have ice water for cross country practice after school.  Water is great ice water is a luxury. My wife takes hot coffee to school and there it is still hot at the end of the day. Ice water will still have some ice in it after 24 hours and hot beverages will still be hot after 12.

Once you start using one of these you'll just keep coming up with more uses. Cold weather hike — hot broth, bag a special peak — cold beer.

Of all the water bottles we have these two are the only ones that don't ever get put away. We are always finding uses for them.

Source: bought it new
Price Paid: $30

Really one of the best bottles I've used. It's made from stainless steel and is vacuum insulated. Unlike other bottles I've used, the Hydro Flask doesn't sweat or get cold when I put ice cold water in it. It keeps cold stuff cold and hot stuff hot like an old-school thermos. 

I use it for hiking, biking, and camping. And I use it for my cold water or hot coffee.

Price Paid: $25

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Price Current Retail: $20.57-$34.95
Historic Range: $15.63-$85.80
Reviewers Paid: $22.00-$30.00
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