HydraPak UltraFlask Speed Review

Overview

The UltraFlask Speed is HydraPak’s collapsible 600 ml soft flask. It’s a TPU bladder with a 42 mm mouth and a flip-open SpeedFill cap, built for runners who want faster refills at aid stations. Long-distance hikers have adopted it for the same reasons: it weighs 46 g, rides in a shoulder-strap pocket, and shrinks as it empties. The trade-off is durability. The cap is quick but only snaps shut, and owner reports of leaks at the cap threads or valve are common enough to matter on a long trip.

Key Specs

Spec	Detail
Capacity	600 ml (20 fl oz)
Weight	46 g (1.6 oz)
Dimensions	186 × 81 mm (7.3 × 3.2 in)
Material	TPU with RF-welded seams; HDPE cap components
Opening	42 mm SpeedFill cap
Cap options	Direct-mount bite valve or 100 mm (4 in) straw cap
Filter compatibility	Fits HydraPak 42 mm filters and bite valves
Max temperature	60 °C (140 °F)
Freezer-safe	Yes
BPA/PVC	Free of both
Care	Hand wash

Performance

Refilling. The SpeedFill cap is the reason this flask exists. A side tab pops the cap open in one motion, and it clicks shut again. That means no threading and unthreading a lid with cold, wet fingers at a stream or a race aid table. The 42 mm mouth is wide enough for ice and drink mix. HydraPak’s own buyers describe the flip-cap as a time-saver, though some say it’s easy to spill if the fill is rushed.

Carry and bounce. The flask is soft and shrinks as it empties, so the water has less room to slosh as the bottle drains. It’s designed for vest and strap pockets, and owners report that it sits flat without chafing. One long-distance hiker found the 600 ml model fit a Gossamer Gear Bottle Rocket sleeve well across its width but wished it were an inch or more taller. Buyers with Instinct running vests report it as a clean swap for the proprietary flasks those vests ship with, and it lets them use HydraPak filters.

Drinking. Two cap styles ship with the flask. The direct-mount bite valve suits a vest pocket. The 100 mm straw cap lets a flask sit upside down in a chest pouch and be sipped without pulling it out. The bite valve auto-seals to stop drips. Because the flask collapses as it drains, it doesn’t build up a vacuum, which is why these caps don’t need a separate air valve.

Weight in context. The 46 g figure is for the flask with cap, as HydraPak lists it. A hiker who weighed the parts separately recorded about 23 g for the empty 600 ml flask body, with a direct-mount cap adding roughly 13 g and the extended straw cap about 20 g. For comparison, the same hiker weighed an empty 500 ml Smartwater bottle with sport cap at 29 g. The weight savings over a disposable bottle are real but modest. The gain is in packed volume: the flask folds into a ball when empty.

Filter compatibility. The 42 mm thread accepts HydraPak’s filter caps, as well as Seeker and Flux bottles. That makes the flask a workable dirty-water or clean-water pairing with a 57 g filter, which HydraPak describes as one of the lightest on the market.

Durability and care. Ratings are strong. The 600 ml model averages about 4.5 stars across retailers, and roughly four in five reviewers on one large retailer’s listing gave it five stars. The complaints are consistent, though. HydraPak’s own review summary for the sister 500 ml model notes several owners with leaks near the cap threads or from detached valve nipples. One buyer pointed out that the SpeedFill cap doesn’t lock past its snap and could pop open in rare cases. Some owners report an initial plastic taste that fades with cleaning. Hand washing is recommended, and the flask can be frozen. Heat is capped at 60 °C, so it shouldn’t be filled from a boiling pot. HydraPak backs the line with its Beyond Lifetime Warranty.

Pros & Cons

Pros

• 46 g with cap, and it packs to a fraction of its filled volume
• One-handed SpeedFill cap with a 42 mm mouth for ice and powder
• Shrink-as-you-drink design cuts slosh in a pocket
• Direct-mount bite valve and straw cap both included
• Fits HydraPak’s 42 mm filters and bottles
• Strong owner ratings, with the brand’s warranty behind it

Cons

• Cap snaps rather than locks, so it can open if jostled
• Owners report leaks at the cap threads and from detached valve nipples
• At 186 mm tall, it can sit short in tall bottle sleeves
• Some owners notice an initial plastic taste
• 60 °C ceiling rules out hot fills
• Hand wash only

Who Should Buy This

Trail runners, fastpackers and thru-hikers who carry water in shoulder-strap pockets or a vest will get the most from it. It also suits anyone building a light filter setup around a 42 mm thread. Hikers who stuff their bottles loose into a pack where the cap could be bumped open, and anyone who needs a bottle to survive years of rough handling, should look at a rigid bottle like a Smartwater. Cold-soak and hot-drink users should pick something that tolerates more than 60 °C.

Verdict

The UltraFlask Speed does what it was built to do. It’s light, it packs small, and its cap makes refills fast. The cap’s snap closure and the leak reports at the threads keep it from being a set-and-forget choice. Buy it for vest or strap-pocket carry and check the cap before each long carry.