A water bottle that goes unnoticed is a good thing in our book. That means it’s keeping you hydrated without any mishaps or requiring any fussing. But we can also appreciate good aesthetics. Hydro Flask, in particular, has built a loyal following with vacuum-insulated bottles that sport unmistakably bright powder-coated exteriors and keep whatever’s inside cold or hot, so you can quench your thirst while on the trail, sip hot coffee all morning long, or take a swig while running errands around town. We tested some of the company’s most popular drinkware (and helpful add-ons) and here’s what rose to the top.
Read quick info here on the top-performing Hydro Flask thermoses and accessories, then keep scrolling for buying advice and in-depth reviews of these and other models.
What’s All the Hype About?
Vacuum-insulated drinkware dates back to the 1890s when Scottish physicist and chemist James Dewar invented the vacuum flask. The container had an inner and outer wall separated by a vacuum. Air is highly effective at transferring heat, so by removing it, any liquid inside a sealed double-walled vessel will retain its initial temperature for longer. The first thermoses were made with glass, but sturdier stainless steel has won out.
Unlike many competitors, Hydro Flask stands out with its colorful bottles that are available in multiple sizes, styles (including a growler), and for various purposes. And thanks to user-friendly insulated lids, these bottles offer a better drinking experience than a traditional thermos with a screw-in cap while still providing excellent thermal retention. The insulation used in many of the lids mimics the architecture of a beehive. Trapped air inside each of the hexagonal pockets reduces air circulation and, in the process, heat transfer. Backed by this double-insulated construction, the brand promises most Hydro Flask bottles can keep beverages cold for up to 24 hours or hot for up to 12. Those stats are on par with similar products but still impressive. Early on, the Oregon company even shipped Hydro Flasks full of ice across the country to get noticed by dealers.
Care and Use
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.
You’ll get the best thermal performance by putting your Hydro Flask in a place that’s cool when it’s filled with something cold or a place that’s warm when it’s got something hot inside. In the heat of summer, your ice water will last a lot longer if the bottle is in the shade instead of direct sunlight. Likewise, don’t expect your coffee to stay hot for hours if you leave your travel mug on a snow-covered sidewalk as you shovel the driveway. A little common sense goes a long way in reducing the rate at which your Hydro Flask will reach temperature equilibrium with its surroundings.
How We Tested
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:
The hot test: We filled each thermos to the very top (as high as we could without spilling) with boiling water and measured the starting temperature with an infrared thermometer. We then closed the lids and let them sit for 24 hours. Before opening, we shook them to distribute any hot water that may have risen to the top, then tested each with that same thermometer. After emptying the bottles, we let them sit for three hours so all parts would return to room temperature before continuing to part two.
The cold test: We filled each bottle to the brim with chilled water before measuring the temperature. Again, we sealed up the bottles and let them sit for 24 hours. The next day we shook them, opened each, and checked the temperature once more.
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.
DRINKWARE —BEST OVERALL—
Hydro Flask 40-oz Wide Mouth
Weight: 1 lb 2.3 oz | Heat loss (hot test): -76.5℉ | Heat gain (cold test): 3.4℉ | Other sizes: 20, 32, and 64 oz
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.
—BEST FOR COFFEE—
Hydro Flask 16-oz Coffee with Flex Sip Lid
Weight: 11.9 oz | Heat loss (hot test): -91.5℉ | Heat gain (cold test): 7.7℉ | Other sizes: 12 and 20 oz
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.
—LIGHTWEIGHT AND LARGE—
Hydro Flask 32-oz Wide-Mouth Trail Series
Weight: 12.4 oz | Heat loss (hot test): -80.7℉ | Heat gain (cold test): 3.5℉ | Other size: 24 oz
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.
—BEST FOR HOT BEVERAGES—
Hydro Flask 21-oz Standard Mouth
Weight: 12.1 oz | Heat loss (hot test): -63.7℉ | Heat gain (cold test): 8.1℉ | Other sizes: 18 and 24 oz
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.
—BEST FOR HYDRATING AT HOME—
Hydro Flask 22-oz Tumbler
Weight: 12.2 oz | Heat loss (hot test): -107.2℉ | Heat gain (cold test): 14.4℉ | Other sizes: 16 and 32 oz
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.
ACCESSORIES —BEST LID—
Hydro Flask Wide-Mouth Straw Lid
Compatible with: Any wide-mouth Hydro Flask | Other size: None
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. (We didn’t repeat the hot test because Hydro Flask recommends this lid for cold beverages only.) It’s also not leakproof, according to the company, though we didn’t notice any drips or leaks when we turned the bottle upside down and shook it. Given its popularity, Hydro Flask also sells its 32-ounce and 40-ounce bottles with straw lids instead of screw-tops that will save you a few bucks compared to buying this lid separately.
—FOR EXTRA PROTECTION—
Hydro Flask Medium Flex Boot
Compatible with: 32 and 40 oz Hydro Flask bottles | Other size: Small (for use with any 12–24 oz Hydro Flask bottles)
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.
Shop Medium Flex Boot | Shop Small Flex Boot