HydraPak UltraFlask+ Filter Cap

What it removes from water, and how well that is proved. 8: Clearly better than most.

0.2 µm hollow-fibre filter. HydraPak's fact sheet (for the UltraFlask+ flask with this cap) names the EPA Guide Standards and NSF P231 for bacteria and cysts: a named standard for bacteria and protozoa at 0.2 µm, which is the Protection 4 line. The shop page gives slightly different percentages and cites HSF 42, so we use the fact sheet. No virus claim, so not 5.

How fast clean water comes through when it is new. Real flow drops as it clogs: see Ease of use. 4: A bit below average.

HydraPak gives "more than 1 L/min", so we band 1 L/min, which is 0.6 to 1.19. Adventure Alan says the flow is very high when new but falls to about half as particles build up, and lists this cap as the slowest of its peers. Banded on HydraPak's figure.

How much it adds to your pack. 10: The best you can buy for this.

HydraPak UK sells this cap on its own, at 36 g, under the 90 g line, so that is the weight we band (band 5). You need a flask with a 42 mm neck, which is not included: HydraPak gives 65 g for its own 500 ml UltraFlask+ flask and cap together (i-Trekkings weighed 84 g), which is still band 5. Ultralight Outdoor Gear lists 35 g.

Filling, squeezing or pumping effort, how fast it clogs in peaty or silty water, and how easy it is to clean. 8: Clearly better than most.

Adventure Alan (3) tested the UltraFlask+ with this cap and calls it the best squeeze filter for trail running: its bite valve is fastest to drink from and it cleans by swishing or by the tiny backflush adapter. It is awkward for filling other containers and the valve can leak if pressed. i-Trekkings (4, flask and cap sent free by HydraPak) used the 500 ml flask with this cap for 18 days: very intuitive, easy to clean, but it leaked a little from the valve when squashed in a pocket and the reviewer could not make the backflush adapter work. For both, we count only what they say about the cap (valve, flow, leaks, cleaning), not the flask. Filter-only source: Better Trail (5) tested the sister 42 mm filter cap, not this one, so we count only what it says about the filter itself (attaching it, flow, cleaning); Adventure Alan says the filter is the same as the 42 mm cap's. Average 4 out of 5, so 8 out of 10.

Reviewers disagree on this.