Thursday, October 02, 2025

Hydrapak Flux™1L Collapsible Bottle & 42mm Filter Cap Review: Clean, Safe, Tasty Water Anywhere!

Article by Dominique Winebaum

Hydrapak Flux™1.5 L & 42mm Filter Cap (Bundle $69) 42mm Filter Cap ($40)

I used the Hydrapak Flux™1L paired with 42mm Filter Cap as my hydration gear when trekking on the Tour des Combins (see Trip and Gear Report here).  Sam featured the 42mm Filter Cap in the 2024 RoadTrailRun gift guide: 

Sam: This 42ml size filter fits on many HydraPak soft run flasks as well as larger foldable 1 liter versions, so it is interchangeable including to other 42ml flasks.  Its filter removes 99.99% of E Coli & Parasitic cysts  and can filter approximately 1,500 liters of fresh water at a rate of >1 L per minute. It can also  be used to fill other bottles with filtered water, just squeeze.  It has a handy snap cover over the nozzle to keep our dust and prevent leaks.  I used it daily for 9 days during a trek in France, for many runs and for travel.  The 42 Filter Cap is available separately or with a Hydrapak flask and is a great gift idea for any runner, hiker, or traveler. 

I typically carry an hydration reservoir/bladder when hiking or trekking, however, I enjoyed the benefits of an Hydropak Flux & 42 mm Filter Cap on our TDC:

  • The collapsable bottle weighs half the weight of a regular hard plastic bottle

  • I carried the Hydrapak Flux in one of the side pockets, which was easy to retrieve









  • I would refill my Hydrapak with fresh and cold water from fountains and stream in confidence the filtered water would be safe, thanks to the filter cap

  • Some of the huts warned against drinking the water from the tap and would charge 6 Swiss Francs per water bottle.  I was able to get free water from the tap thanks to the filter cap 

  • The collapsable bottle takes less room when empty than a regular water bottle

  • I did not have to fuss (or worry with a bulky hydration reservoir in my backpack

  • The water tasted great and I drank plenty of it on our trek


I very much liked the 1 L capacity for our trek and learned to trust my 42mm Filter Cap when refilling from a stream, uncertain fountains and taps and day day out for travel, work, and activities as the filtered water tastes so good. 


Note in 2025 the bundle flask is now 1.5 L. We tested a 1L version.


All of Hydrapak’s  Filtration gear including Filter Caps for bike squeeze bottles and as well as a filter with a non flip top running type nozzle are available at Hydapak HERE


Thanks for reading our review!
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Dominique has run for over 45 years, consistently about 25 miles per week at paces between 11 and 12 minute miles and once a week down in the mid 9 minute miles. She races rarely, but always surprises more hard core runners in her age group when she does. She has a 1985 marathon PR of 3:16 in her second marathon which at the time put her on the top 10 Swiss women’s lists. An avid hiker and trekker, she has been around Mont Blanc 3 times, hiked Chamonix to Zermatt, and completed the 48 New Hampshire 4000 footers. She is the mother of two grown children, both runners post college, and also enjoys nordic and alpine skiing, tennis, and gardening. 


Samples were personal purchases. No compensation was provided by brands for writing this article. RoadTrail Run does have affiliate partnerships and may earn commission on products purchased via shopping links in this article. These partnerships do not influence our editorial content. The opinions herein are entirely the authors'.

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