Analysis of HydraPak UltraFlask + Filter Cap
First of its kind bite valve squeeze unit is easily the best filter for trail running
What separates the new-for-2025 HydraPak UltraFlask + Filter Cap from its competitors is the fact that it is the first and only squeeze filter with a bite valve. And thanks to UltraFlask’s narrow cylindrical shape, it is also the best fit for front-mounting into a running vest pocket. Going forward, we expect this to become the gold standard for trail running hydration.
- Price: $50
- Volume: 500ml
- Weight: 2.3 oz (when dry)
- Competitors: Katadyn BeFree AC, LifeStraw Peak Squeeze
- Pros: Best filter for trail running. Smallest and lightest among peers. Best shape for front mounting and vest pockets. Bite valve is fastest to drink from. Swish and backflush cleanable. Minimalist backflush component mates with any 28mm bottle.
- Cons: Bit valves can release water if pressured, ergo don’t store inside of a pack or at your feet in the tent. Awkward to use for filtering into other vessels. Rated for shortest lifespan, slowest flow. TPU plastic taste at first.
Compare to its peer group in our guide to the best soft flask squeeze filters.
Editor’s Note: At time of publication, the HydraPak UltraFlask + Filter Cap is brand new. If any of our analyses should prove incorrect after a full season of use, we will update this review accordingly.
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Overview: Soft Flask Body, Filter, Bite Valve, and Cleaning
To clarify, this is nearly, but not quite the same HydraPak UltraFlask as you already know and love. It features the same collapsible 500ml TPU body, but with an extra half inch of reinforced hard plastic at the shoulders to stabilize the submerged filtration unit. Compared to its peers, it fits best in running vests and shoulder strap pockets. The bite valve is also identical to the baseline UltraFlask, but the flow rate is a smidge slower as water must also pass through a filter.
The hollow fiber filter with plastic casing component is a Katadyn BeFree clone, and identical in shape and structure to HydraPak’s first 42mm filter, only with a bite valve instead of the twist/flip top. That’s to be expected as these companies share technology with each other (did you know Katadyn BeFree uses a HydraPak brand soft flask?).
The flow rate is extremely high at first! But like BeFree, it degrades with use overtime, hitting a steady state somewhere around half of its original flow rate as particles build up in the system.
HydraPak UltraFlask + Filter Cap’s biggest drawback is that it is the least effective unit at filtering water into other vessels. To do this, you must either squeeze the bite valve while holding the soft flask, or temporarily remove the bite valve. Both options are wetter experiences and give less control and add fussiness compared to Katadyn BeFree and LifeStraw Peak Squeeze.
Something we found really unique and cool about the HydraPak UltraFlask + Filter Cap is the dual cleaning mechanisms. Like Katadyn BeFree, it can be swish-and-shake cleaned easily while on the go to dislodge particles and immediately improve flow rate by a small to medium amount.
For heavier duty cloggage, it also comes with a backflush tap that we’d actually want to carry into the backcountry. Unlike a Sawyer or LifeStraw syringe, this component is tiny and virtually weightless. To use it, remove the bite valve from the head of the UltraFlask, and screw the backflush tap onto any 28mm head bottle (AKA Smartwater). Plug the tap into the top of the filter where the bit valve was, and squeeze the bottle to flush water backwards through the filter. Voile, improved flow rate! This is another great differentiator from the peer group – Katadyn BeFree AC can only be swish/shake cleaned, while LifeStraw Peak Squeeze can only be flush cleaned.
HydraPak UltraFlask + Filter Cap Vs Katadyn BeFree AC
In this section, we compare relative pros and cons of HydraPak UltraFlask + Filter Cap vs Katadyn BeFree AC. To generalize, the HydraPak UltraFlask + Filter Cap is better for trail running, since its narrower chassis fits better into vest pockets, and its bite valve is faster to drink from on the go. On the other hand Katadyn BeFree AC is better for hikers and backpackers because it is better for filtering into other vessels and more spill proof, ergo it can be stored inside of a pack or the floor of a tent without worry, not just front mounted. See more in our guide to the best soft flask squeeze filters.
Relative Advantages of HydraPak UltraFlask Filter vs Katadyn BeFree AC
- Bite valve is faster and easier to drink from
- Narrower cylindrical body with less bulky head fits better into running vest and shoulder strap pockets
- 0.3 ounces lighter weight
- Slightly thicker TPU
Relative Advantages of Katadyn BeFree AC vs HydraPak UltraFlask Filter
- Cap is more spill-proof, unit can be stored anywhere in pack or in a tent without worry of leakage if pressured by other objects
- Easier to use for filtering into other vessels
- Available in 0.5L and 1.0L sizes
- Removable activated carbon filter for taste enhancement
- Has clip attachment point
- $5 less expensive (for comparably sized version)
HydraPak UltraFlask + Filter Cap VS LifeStraw Peak Squeeze
In this section, we compare the relative pros and cons of HydraPak UltraFlask + Filter Cap vs LifeStraw Peak Squeeze. To generalize, the UltraFlask’s body is better shaped for front mounting, and it’s bite valve is faster to drink from on the go, making it far superior for trail runners. On the other hand, LifeStraw Peak Squeeze is less prone to spillage, better for filtering into other vessels, more durable, and costs less money. See more in our guide to the best soft flask squeeze filters.
Relative Pros of HydraPak UltraFlask + Filter Cap
- Bite valve is faster to drink from on the go
- Narrower body front-mounts much better in running vests and shoulder strap pockets
- 1.3 oz lighter weight
Relative Pros of LifeStraw Peak Squeeze
- Spill-proof cap means unit can safely be stored inside of a pack or on the floor of your tent
- More durable
- $12 less expensive
- Slightly higher volume (if desired)
- Rated for longer filtration lifespan and faster flow rate
Left: HydraPak UltraFlask + Filter Cap. Right: Katadyn BeFree AC
HydraPak UltraFlask Filter Review Conclusion
HydraPak UltraFlask + Filter Cap is the new gold standard in trail running filtration-hydration thanks to its easy-to-use bite-valve and vest-pocket-accommodating shape. Despite being less spill proof and more awkward for filtering into other vessels than competitors like Katadyn BeFree AC and LifeStraw Peak Squeeze, it’s so efficient that hikers should also consider choosing HydraPak UltraFlask + Filter Cap. Happy hydrating!
