Hydro Flask 18 oz Standard Mouth Bottle with Flex Cap
An 18 oz insulated bottle that fits a daypack side pocket
An 18 oz (532 ml) standard-mouth stainless bottle with a Flex Cap and TempShield double-wall insulation, rated 24 hours cold and 12 hours hot. Leakproof when closed and BPA-free.
Our take
Bigger isn't always better with bottles. On a city day, a big bottle is just weight you haul from the museum to lunch. 18 oz slips into a daypack side pocket and still keeps water cold for up to 24 hours or coffee hot for 12.
It's leakproof when closed, so it can ride inside your bag on the train. The stainless steel means no flavor transfer, and it's widely reviewed. The catch shows up in heat or on a trail. 18 oz runs dry fast, and you'll be hunting for refills. The standard mouth also makes adding ice slower.
For city breaks and commutes, this is the one we'd buy. For hikes or hot places, get a 24 to 32 oz bottle instead. Check the price before you book.
Who it’s for
City travelers and commuters who want a compact bottle for cold water or hot coffee.
Skip it if
Skip it if you hike or travel somewhere hot. A 24 to 32 oz bottle means fewer refill stops.
Hydro Flask 18 oz Standard Mouth Bottle with Flex Cap: questions people ask
What size water bottle is best for travel?
For city days, 18 to 24 oz is easy to carry and refill. For hikes or hot climates, 32 oz or more keeps you from running dry.
Can I take a full water bottle on a plane?
Not through US security. Empty it before the checkpoint and refill at a fountain once you're through.
Can an insulated bottle keep coffee hot?
Yes. Hydro Flask rates this one for up to 12 hours hot, so your morning coffee stays warm through the day.
Where we recommend it
More in Water Bottles & Hydration
Hydro Flask 24 oz Wide Mouth Bottle with Flex Straw Cap
The right size for road trips and city days, but the straw lid is more work to clean in a hotel sink than a screw cap.
Nalgene 32 oz Wide Mouth Bottle
A tough, light quart for hikes and road trips that pairs with many water filters, but it isn't insulated and the wide mouth splashes on the move.
Nalgene 32 oz Narrow Mouth Bottle (Amethyst)
Spills less than the wide-mouth version when you drink on the move, but many water filters won't fit and ice goes in slowly.
Prices change often — the price on the retailer’s page is the one you pay.