Eschewing fancy names, HydraPak adds their own filter to the small but growing choice of 42mm water filters that will connect to wide mouth bottles, bladders and flasks.

Long term readers will be aware that Three Points of the Compass has long been a fan of the BeFree water filter. Manufactured by Swiss based Katadyn, the BeFree was first released in 2016 and I purchased one the following year. It and its replacements have been on the very great majority of my multi-day hikes since then. I like to leave a filter permanently attached to whichever of the flexible TPU bladders or bottles I take on trail. This is usually a two-litre ‘dirty water’ Seeker bladder made by HydraPak. Occasionally it might get swapped out for a one-litre flexible bottle. I can then either drink directly from this, or squeeze filtered water into my cookpot, or more normally, into my drinks bottle or Evernew ‘clean water’ bladder. Infrequently, I have rigged it up as a gravity system, usually when the filter membranes have become clogged and water has slowed to a dribble. Note that the various soft bottles supplied by Katadyn with their BeFree filter are made for them by HydraPak. Established in 2001, HydraPak have produced a wide range of flexible water containers of various capacities and in 2023 they released their own brand filters to fit these, though we had already seen it under another name, more on that below.

On 31 January 2023, HydraPak announced the release of their own brand of micro-filters. One is a 28mm Filter Kit, however I was more interested in their other filter. The full name for this is the HydraPak 42mm Filter Cap ‘filtration accessory’. Unsurprisingly, it is fairly similar in design to the BeFree, but is slightly longer, with a very different cap. The twist nozzle on the cap has a hinged dust cover that can be operated with one hand. It is compatible with all of HydraPak’s 42mm neck flasks, bottles and bladders. We are seeing an ever-growing choice of these wider neck bottles and bladders come to market, and I prefer them as they are easier to fill from rivers etc.

This filter from HydraPak had previously been seen in another guise and it looks as though HydraPak were, quite literally, testing the waters (and customer feedback) in advance of their own release. In Spring 2020 Salomon announced the release of their Salomon Soft Flask XA Filter. Careful study of the XA filter and the new offering from HydraPak reveal that the filter body and cage/frame are identical lengths and construction, with identical injection mouldings, while the screw neck and mouth piece differ.

I do not know if Swiss based Katadyn make their BeFree filters in-house or if they are made for them elsewhere, which I suspect is the case, however the 42m Filter Cap is made for US based HydraPak by Diercon Technology Limited. This long established Chinese manufacturer is responsible for a number of portable water filters you will find on Amazon and elsewhere. (EPA Company No.:102123. EPA Establishment No.: 102123°CHN°1).

HydraPak inform us that this filter will effectively remove common waterborne bacteria, such as E. coli (99.9999%), parasitic cysts (99.999% on packaging and accompanying Owner’s Guide, or 99.9999% on the online Fact Sheet) and microplastics (99.999%). It will not remove viruses. For that, you need to boil water, or combine filtering with either chemical sterilisation, or use a larger/heavier Grayl filter. There is another alternative, the newly released Pure Clear Collapsible Squeeze, uses the same technology as the Grayl filters and does remove viruses. I’ll be looking at that filter in a future post. In common with all of these hollow fibre filters, the HydraPak offering has a limited life. The BeFree is advertised as having a life of up to 1000 litres of water and we are advised that the 42mm Filter Cap is OK for up to 1500 litres, but expect performance to fall off dramatically before it gets anywhere near this figure. When new however, flow rate is impressive and is in excess of a litre a minute.

The 42mm Filter Cap is primarily a squeeze filter that utilizes hollow fibre technology. The drinks cap is (obviously) outside of the bottle/bladder, standing just proud of the neck, mounted on a hard plastic ring that is screwed onto the 42mm wide opening of the bottle. This is smooth and lacks any corrugations or ridges that would aid grip. The identical filter in the Salomon XA alternative has decent moulded ridges in the screw cap that aid grip. The business part of the filter, the hollow fibre membrane, is looped and exposed within a plastic cage that protrudes inside the bottle. The long looped fibre strands have tiny 0.2 micron holes (0.0002 mm) that capture cysts, bacteria and sediment as turbid water is squeezed through them. This method requires soft sided water containers to achieve this, it cannot be used with rigid containers.

The 42mm Filter Cap is 100% BPA and PVC Free. While HydraPak do not reveal the specific materials used in their filter, instead being a bit generalist, the previous incarnation of this filter, the Salomon XA, did tell us that material used for that product, with a silicone bite valve, are: 40% Thermoplastic Polyurethane, 21% Acrylonitrile-Butadiene-Styrene, 21% Polyoxymethylene, 11% Polysulfone and 7% Silicon. We can infer a great deal from this. The whole cap is a one-piece unit that cannot be disassembled. The filter element cannot be removed from the cap or replaced and the entire filter has to be replaced at the end of it’s life.

HydraPak advertise the filter as weighing 57g (5.7g on their Fact Sheet!) which is a little surprising as it actually weighs 41.6g (dry weight). Note that the BeFree weighs 34g (dry weight). The Salomon XA filter weighs 36g but that has a simpler bite valve with no dust cap. 42mm Filter Cap is 103mm long, with the cap closed, though much of this length is inside the water container when screwed on. The cap has an extreme width of 48mm and thread size of 42mm. The exposed filter body is 77mm long though only 60mm of this plastic cage has cut-outs to allow water to flow around and through the internal filter membrane. By comparison, the Befree has an exposed cage of 62mm of which 52mm has cut-outs. So, the HydraPak product has more of the filter membrane exposed than the BeFree, which allows for an improved flow rate.

The flow rate is impressive at greater than a litre a minute. But in common with all of this type of filter, expect this to fall off as it gets clogged with debris, particulate matter or calcifies. Regrettably, the 42mm Filter Cap cannot be backflushed. This really should have been an option as most people complaining about the similar BeFree fail to see why it cannot be done when the Sawyer filter can be backflushed and HydraPak would have taken a certain percentage of the market if they had made this possible. Instead, it has to be swished around in clean water, or have a solution of 500ml water (filtered or treated) with four drops of added bleach, put through it. Once wet, this filter should not be allowed to freeze. If it does, expanding water within the hollow fibre membranes can cause them to split, allowing contaminants to pass through. If it does freeze, or is suspected of having frozen, there is no reliable integrity test and the filter should be replaced. Keep it inside the pack on below freezing days and inside the sleeping bag at night.

The twist cap works well, It is less than half a rotation from closed to open and the plastic flip cap opens and closes easily with the tip of a thumb or finger. If the flip cap were broken it cannot be replaced or repaired though the twist drinks nozzle could still be rotated. I also cannot see a way of making this into a gravity system as there is no way to connect to it. It is an odd decision by HydraPak to make this cap a single use affair and it would have been good to see some way of attaching a hose or threaded container to it.

I purchased a stand alone 42mm Filter Cap to use with one of the HydraPak water containers I already have. It cost me £34.27 via Amazon. It is also available as part of a ‘system’. The FluxTM+1.5L, combined with a newly released 1.5 litre HydraPak bottle, or as the SeekerTM+3L, combined with a 3 litre bladder. I wouldn’t be surprised if the options increased and would like to see the filter also offered with their 1 litre bottle and 2 litre Seeker bladder.

1.5 litres isn’t far off the 2 litre capacity of the dirty water bladder I have been using for the past six years and I might just find myself preferring the slightly smaller capacity. The Flux bottle also has a tougher, two layer, construction instead of the single skin Seeker, and while I have never had a 2 litre Seeker bladder puncture on me, other people have, and I do like the idea of increased durability here. Another bonus is the flexible Flux bottle stands up, which the two-litre Seeker bladder cannot do. So I am also trying out the FluxTM+1.5L combination over the next few months. This combination duo cost me £42 via Amazon, which is pretty good value compared to the cost of my single filter by itself, though is still a fairly expensive purchase. I’ll be reporting back on how I have got on with it and whether I will permanently switch from 2 to 1.5 litres for my dirty water container. The increased weight is a little concerning to me as I don’t like to increase this when making changes to my gear. Dry weight of the filter with my older first generation 2-litre Seeker bladder is 103g. Dry weight of FluxTM+1.5L is 141g (advertised weight 143g).

The number of hollow fibre filters on the market has steadily increased over the past few years. I don’t know how long the Salomon XA filter will remain available but it would have once been advisable to snap up that option while it is still around as it has the same technology as the new HydraPak product, is lighter and has a simpler bite valve with less to go wrong. However, the XA filter has risen considerably in price since first release, so may have now priced itself out of the market.

Many of these filters are suitable for lightweight backpacking and they come in various formats- as drink straws, as 28mm and 42mm thread size, or as inline filters. Beside the 42mm Filter Cap, HydraPak also sell a filter that can be simply inserted into one of their Plug-N-Play bottle caps. Sawyer remains a favourite 28mm filter for many, and I have used them myself. However these require some form of adapter to fit my favoured wide mouth bladders. I suggested how this can be achieved in two posts on the subject.

• Converting a 42mm neck HydraPak bladder to fit a 28mm water filter- the hack
• Converting a 42mm neck HydraPak bladder to fit a 28mm water filter- Plug-N-Play

The Filter Fact Sheet can be seen here, and the online User Manual, that also comes hard copy with each filter, can be seen here.