About Hydro Flask
I have a work-from-home morning ritual. I wake up, go downstairs, and make my morning coffee in a specific white mug. Then I attend to plant mom duties. I water the tomato plant. I water the ficus. I don’t water the succulents, but I poke at them to check in.
When I’m happy with the hydration status of my quarantine plant family, I grab my own water bottle—a simple, clean-lined Hydro Flask. It has to be those things, in that order, and that bottle, or I can’t start my day.
The Hydro Flask 21 oz Standard Mouth water bottle has been a favorite since we began testing water bottles in 2013. It doesn’t leak, unlike many bottles we’ve tested. The lid takes no more than a turn-and-a-half to remove, and the lip of the bottle is thinner than most. The flexible handle accommodates your hand without getting in the way.
Overview of Hydro Flask
Hydro Flask bottles are built to last—something I can personally attest to. I got my first Hydro Flask about five years ago and have toted it around just about everywhere, including trails, city streets, gyms, airports, and train stations.
I’ve dropped it more times than I can remember, and after all that abuse, it’s managed to pick up only a few dings and still keeps my water icy. That said, it’s probably best not to follow my lead.
Drop or bang around any thermos and you run the risk of breaking its vacuum seal. As for cleaning, Hydro Flask announced in 2020 that its new bottles and lids are dishwasher-safe.
If you’re washing by hand, a bottle brush will come in handy. It’s also a good idea to deep clean the lid every so often by removing and scrubbing the silicone gasket in hot, soapy water. Let it dry completely before reinstalling it to prevent any mold from forming.
Hydro Flask Product Review
To find the best Hydro Flasks, we compared six bottles of various shapes and sizes and seven styles of lids, considering the cost, weight, usability, and insulating performance of each. We assessed insulation as follows:
Using these measurements, we calculated the heat loss for our hot test and heat gain for our cold test. In both cases, a smaller number is better.
We also used these bottles as you will, seeing how easy they are to drink from, close, open, toss into a bag, and clean. We wanted to see how well they’d fit into our life to know how well they’ll fit into yours.
Hydro Flask 40-oz Wide Mouth
If there’s a bottle to rule them all, it’s the 40-ounce Wide Mouth. The large capacity provides plenty of space for hydrating water and leaves you enough room to bring hot cocoa to share after getting in some turns at the local ski resort.
The wide opening let in small and large ice cubes without a fuss. Moreover, this bottle touts excellent thermal retention and came in second during the hot and cold portions of our temperature test.
Although the boiling water cooled significantly, it was still noticeably warmer than room temperature after 24 hours. Similarly, the refrigerated water remained cool and refreshing. North of one pound to start, this bottle only gets heavier the more you fill it.
And don’t expect the wider base to squeeze inside backpack water bottle pockets that don’t have any elastic. Still, from a performance perspective, you won’t find its equal. Don’t need the high-volume capacity? Choose the similar 32-ounce Wide Mouth that measured just behind the 40-ounce version in our thermal testing.
Hydro Flask 16-oz Coffee with Flex Sip Lid
For many years, Hydro Flask touted its cold retention as one of its hallmarks, without focusing much on vessels designed primarily for hot drinks. But that changed in 2020 with its Flex Sip Coffee collection.
The wide-mouth bottle design was downsized, and best of all, Hydro Flask replaced its unremarkable flip lid (which wasn’t leakproof) with a twist-open model that didn’t unleash hot coffee when we flipped it upside down or carried it in a backpack.
We liked that liquid emerged in a smooth, steady flow instead of the staccato rate you get with some other coffee lids. The sipping convenience does have tradeoffs: only average temperature retention (true of all travel mugs) and a somewhat complex lid design when it comes time for cleaning. We weren’t confident that a simple scrub and rinse actually cleaned the lid.
Instead, we separated it into its four parts, gave it a good wash, and needed to refer to the directions the first few times to remember how to put it back together properly.
It got easier the more we did it. As for the heat retention, we found our coffee was still hot enough for our liking five hours after we filled the thermos one day. Unless you’re the type that needs yours piping hot from 9 to 5, it should do just fine.
Hydro Flask 32-oz Wide-Mouth Trail Series
Our biggest gripe about most Hydro Flasks is how heavy they get when full of ice water. It’s still worth it on blazing hot summer days, but heavy is heavy. So we took notice when the company released its lightweight Trail Series last year.
On our scale, the 32-ounce-capacity model weighed 22 percent lighter than the traditional design, thanks to thinner stainless steel walls, aluminum (rather than stainless steel) pivots on the lid, and a perforated carry strap.
Impressively (and unlike some gear made for the ultralight crowd), the weight savings didn’t drag down the bottle’s performance. During our insulation test, the results were on par with the classic 32-ounce bottle.
All that’s to say, the Trail Series is the only insulated bottle of this size that we actually look forward to packing on hikes. If you’re among the ounce-obsessed, this thermos is worth the modest price jump.
Hydro Flask 21-oz Standard Mouth
Looking to keep a large amount of coffee or other steamy beverage hot for hours on end? Go for the standard-mouth bottle. We tested the mid-size model, and it was by far the best in our hot test.
It outperformed the 40-ounce wide-mouth bottle (the second place finisher) by more than 12 degrees. We credit the classic thermos-style lid that threads into the bottle’s neck. It’s got plenty of insulation and less surface area exposed to room temperature.
Surprisingly, it didn’t perform nearly as well in the cold test, but an 8.1-degree temperature climb after a full day is still nothing to scoff at. We liked that the narrower base fit easily into cup holders and water bottle pockets of all sizes. And despite the smaller opening, standard ice cubes fell easily inside when we used it for water.
Hydro Flask 22-oz Tumbler
Because of its double-wall design, the Tumbler didn’t sweat when filled with ice water or become too hot to hold when we had afternoon tea. That’s more than we can say for our regular glasses and mugs.
We liked it best for staying hydrated at home but also appreciated that it still fit in our car’s cup holder. Many tumblers include lids, but Hydro Flask adds insulation to this one, which helped keep our beverages cold or hot for a few hours.
That thermal capacity would have been even better if the drinking spout could be sealed, but that’s not the point of a tumbler. We appreciated that the lip was shallow; it meant we didn’t have to cram our face into the plastic just to get a gulp. Prefer slurping from a straw instead? Pair it with the press-in straw lid.
Hydro Flask Wide-Mouth Straw Lid
A screw-top lid comes standard with most Hydro Flasks, and we don’t have many complaints about it (though on solo road trips, unscrewing the cap can become a dangerous proposition).
But we were quickly charmed by the usability of the Wide-Mouth Straw Lid. Getting a quick sip became as easy as flipping back the spout. The rubber straw has a ¼-inch diameter that provided a high flow rate with minimal effort.
It also separates from the plastic cap for easier cleaning. We were apprehensive about the small finger loop but surprised to find it offered a comfortable enough grip. In this respect, it outperformed the Insulated Sport Cap designed for standard-mouth bottles.
There, the two-finger loop was awkward to hold and interfered with our drinking. What didn’t surprise us is that the Straw Lid sacrifices some thermal performance, but it resulted in less than a degree of difference in our cold test.
Hydro Flask Medium Flex Boot
In our experience, if a Hydro Flask falls to the ground with enough force to leave a mark, that dent or scratch will appear at the base. This 1.5-ounce silicone boot prevents that by absorbing some of the shock and preserving the appearance of your bottle in the process.
Never one to let an aesthetic opportunity go to waste, Hydro Flask offers the simple accessory in a handful of colors: some understated, some eye-catching. It’s not a must-have item, but it can help differentiate your bottle from others and keep it looking good as new for longer.
A few notes on sizing: The boot corresponds with a bottle’s diameter at the base, not at the lip, which means smaller wide-mouth bottles use the small boot. Also, there’s no boot available to fit the 32-ounce Trail Series bottle.
How it works
A double-walled thermos works by eliminating solid conduction between the inner wall and the outer wall, according to Wesley Johnson, a cryogenics research engineer at the Glenn Research Center in Cleveland, Ohio.
A vacuum between those walls stops gas convection from occurring, and so it helps keep cold drinks cold and hot drinks hot.
Other water-bottle manufacturers advertise a copper lining that they claim improves hot/cold retention, but that lining doesn’t actually do much. The Hydro Flask doesn’t have a copper lining, yet our cold water warmed only 9 degrees over 6 hours in our tests.
When to buy
Although we see the occasional sale every other month, the best sales are during springtime and during REI’s Anniversary Sale.