Skip to content

Gear talk: HydraPak flasks

One of the most important rules for successful and enjoyable hiking is efficient hydration. Three Points of the Compass has been looking at some of the products produced by HydraPak, in particular, their Ultraflask.

600ml and 500ml Ultraflasks from HydraPak
600ml and 500ml Ultraflasks from HydraPak

In common with most backpackers Three Points of the Compass has used various hydration ‘systems’ over the years. Usually utilizing one of the two main methods. These are either bladders or bottles. Each method has its positives and negatives. Using a bladder encourages me to drink more as the sipper valve/nozzle is always handy and any time I am thirsty, I can drink with little effort. However it is difficult to keep track of how much water is left in a bladder. Using bottles means that things are almost always lighter, the number of bottles can be increased or decreased as required for various hikes. They can be used for unfiltered/non-sterilised or clean water. However tucking bottles into a pack’s side pockets means effort to take them out and drink. Not a lot perhaps, but certainly enough that it is not ad libitum.

There is a cross-over between the two methods. A handful of manufacturers make converters to drink via tube from a bottle. However neither SmarTube or the Source Convertube will fit much of the HydraPak range of soft flasks that I have been looking at recently. In the past I have tried various options with standard disposable drinks bottles that are possible with the Source Convertube but have not, as yet, found a method that I like.

HydraPak Ultraflask

HydraPak have been producing hydration products since 2001 and Three Points of the Compass has been using their products since 2017, so a recent convert.When backpacking in recent years I have been utilising a 2 litre capacity HydraPak Seeker bladder with an attached BeFree filter for dirty water on longer hikes. I also include a 42g two-litre Evernew bladder for greater capacity of clean water. This is either (reluctantly) carried full or partially full but is primarily for use overnight at camp. Plus one or two disposable plastic bottles, which are usually the smooth sided Smartwater bottles. I say disposable, these bottles last a very, very long time and I have bottles that are over six years old that still work just fine. A single rigid plastic 850ml Smartwater bottle with a sports cap weighs around 35g empty.

A simple hydration kit- two litre 'dirty water' bag with attached filter. Water bottle with flip cap for on the go and a two litre bladder for use in camp or to camel up on drier stretches
Current hydration kit- two litre ‘dirty water’bag from HydraPak, with attached BeFree filter. Smartwater bottle with flip cap and a two litre Evernew bladder for use in camp or to camel up on drier stretches

My dirty water HydraPak Seeker bladder has a 42mm opening for easy filling. It is made from BPA free TPU. It is tough and has never leaked on me. There are various attachment points on the sides and it weighs 111g when including the (wet weight) Katadyn BeFree water filter that is permanently attached to it. I like this method and see no need to change from it. The filter is excellent and swishes clean with relative ease. This is the ‘hydration system’ that I have been looking at recently. I don’t think I can make it any lighter, but possibly a little more efficient. Or perhaps not. Always note however, water itself, is always damned heavy. Not a lot we can do about that other than planning.

HydraPak, Inc. filed a U.S. Patent application for their Ultraflask in 2015 and patent was received May 2018. This is part of their Softflask range. HydraPak are not the only manufacturer producing collapsible drinks flasks, as used by climbers, hikers, cyclists, runners et al. But they have bought many features together in a neat and effective package. I purchased two of the HydraPak Ultraflasks- the 500ml and 600ml, to compare with my existing softflask supplied with my BeFree filter and see which fitted my Gossamer Gear Bottle Rocket sleeve best and also which is most convenient and easily drunk from while hiking.

HydraPak Ultraflasks
Three soft flasks from HydrPak- 650ml soft flask that comes with BeFree filter, 600ml UltraFlask and 500ml UltraFlask
Three soft flasks from HydraPak- Left to right- 600ml soft flask that comes with BeFree filter, 600ml UltraFlask and 500ml UltraFlask
Ultraflask 600ml packaging

HydraPak Ultraflask- this is the 600ml
HydraPak Ultraflask packaging- this is the 600ml

Advertised as being from Oakland, California, the HydraPak UltraFlasks may have been designed there, may even have been packaged there, but they are made in China. Nothing wrong with that. They are easily found on sale in the UK and are extremely affordable. Though obviously not as cheap as a disposable plastic bottle. Colour is never a primary concern for Three Points of the Compass, provided apparel isn’t too garish, but the Ultraflasks do come in a smart, cool looking pale blue.

As with my 2lt Seeker bladder, the 500ml and 600ml Ultraflasks have a 42mm opening, are collapsible and BPA and PVC free,. They are a tough TPU with welded seams. and a fairly rigid screwcap surrounding the top which is gripped while doing up and undoing the cap. Each flask comes with two caps when purchased. I did not have either of these caps previously and they provided further options for experimentation. One is a ‘direct drink mount’ to the cap, the other has a 105mm long extended drink tube cap that can be cut down in length as required. It was the longer drink tube that I was most interested in.

Both caps have auto-seal bite valves that I find I can get a good flow of water through. Unlike drinking from a tube from rigid bottles, the flasks collapse as water is drunk so- no vacuum is caused, if it were, this would prevent water exiting as there is no air valve incorporated into the caps.

This hiking season I have decided to experiment with a bottle holder on my shoulder strap. I have been using the Gossamer Gear Bottle Rocket attached to either the Gossamer Gear G4-20 for longer trips or more recently, on my Osprey Manta daypack for the local hikes we have all recently been restricted to due to Covid. The shoulder straps of my mid-sized Gossamer Gear pack for multi-day hikes do not come over-burdened with loops, straps and daisy chain and there are few options for fixing much to the shoulder straps.

A Smartwater bottle, either 600ml or 850ml, slides straight into the holder. The Bottle Rocket bottle holder is a bit over-supplied with straps and buckles and these frustratingly assist in bringing its weight to 40g completely empty. So I remain on the lookout for something just as functional but less encumbered and a good deal lighter. That will also connect to my pack obviously. But in the interim, this is what I’m using.

850ml SmartWater bottle
850ml Smartwater bottle with sports cap in Gossamer Gear Bottle Rocket shoulder strap bottle holder. The pack is the Gossamer Gear G4-20.

The 500ml HydraPak Ultraflask weighs 21g, the 600ml Ultraflask 23g. Either of these also requires a cap- the extended sipper tube with bite valve weighs 20g and the direct mount cap with bite valve 13g. By way of comparison, an empty 500ml Smartwater bottle with sports cap weighs 29g.

I also had a look at my original 600ml collapsible HydraPak softflask that came with my Katadyn BeFree water filter. While that may be marked up as 600ml, this measurement actually allows for the filter body inside the flask taking up volume. Without a filter and just a normal cap screwed on, it actually holds 750ml. I reckon this is the same product as the ‘SoftFlask 750’ sold by HydraPak. Note that the BeFree filter sold in the U.S. has a 1 litre HydraPak soft flask, a product seen far less on this side of the pond. However, that has a wider base and will not fit the Bottle Rocket. There are other Hydrapak flask/bottle options that the extended tube cap fits but they are either smaller, or will not fit my bottle holder.

But what of the flasks themselves, what does the water taste like? Yes, it can taste a bit ‘plasticky’, though I find the unwanted taste decreases with time. Some hikers add electrolytes and flavourings to their water to disguise or mask any unwanted taste but I simply cannot be bothered. Another thing to note is that a flask in a bottle holder like the Bottle Rocket shields the water from much of the heating up that can happen to bottles exposed to the sun. Never mind unwanted taste, there are few things more unpalatable than overly warm water to drink on a hot day.

500ml HydraPak Ultraflask in Gossamer Gear Bottle Rocket shoulder strap bottle holder
500ml HydraPak Ultraflask in Gossamer Gear Bottle Rocket shoulder strap bottle holder
600ml HydraPak Ultraflask in Gossamer Gear Bottle Rocket shoulder strap bottle holder
600ml HydraPak Ultraflask in Gossamer Gear Bottle Rocket shoulder strap bottle holder
600ml HydraPak/Katadyn BeFree flask in Gossamer Gear Bottle Rocket shoulder strap bottle holder
600ml HydraPak/Katadyn BeFree flask in Gossamer Gear Bottle Rocket shoulder strap bottle holder. This is actually holding 750ml of water

All three collapsible HydraPak flasks fit the Bottle Rocket. This bottle holder has two straps that can be tightened up to ensure a bottle doesn’t come adrift unintentionally. Which is just as well as the slim 500ml bottle slips in far too easily and is too loose. It also extends a handy distance above the holder. However the Bottle Rocket bungee loop that passes over the top of each bottle is also too loose on the 500ml flask. The 600ml Ultraflask fits well width-wise but would have been better if an inch or more longer (taller) but still with the existing diameter. The 600ml (actually 750ml) BeFree soft flask fits possibly the best of the three.

Extended neck and direct connector options on Ultraflasks
Extended neck and direct connector options on Ultraflasks

So why a collapsible bottle and not just a lighter rigid Smartwater bottle or similar? Because of the vacuum mentioned earlier. Without a tube extending to the bottom of a rigid bottle and some form of (often leaking) valve in the cap you can’t drink from a rigid drinks bottle while it is still in situ. However a collapsible bottle crumples as you drink from the sipper lid/valve, circumventing any awkward vacuum. It finally stops delivering when there is around a 100ml of water left in it, easy enough to then take the flask out, loosen the cap and finish those last dregs off, perhaps when refilling it.

a squeeze and easy drinking from collapsible flask
Drinking from direct connecting sipper spout

The simple sipper lid does mean craning the neck quite a bit however and the longer tube positions and orientates the drink nozzle far better nearer the mouth. Another plus point, that I appreciate is that a collapsing flask stops the sloshing around of water in a part full bottle. We then come to another pet gripe of mine. That is the bite valves themselves. I am not a fan of these. I don’t like using them. There are many hikers that feel the same way, those with dentures for example. So I looked at including a better quality and more user friendly drink nozzle on my bottle.

The option is a push/pull valve. Many of these entail using either teeth or fingers to operate. By far the easiest to operate that I have come across is the Israeli made Storm Valve from Source, this is a bit of a favourite with the military and is very well manufactured.

This drink nozzle can be locked by twisting (with the fingers). To just drink from, it is simple to pull open or close with just the lips. The problem with this product is that the valve’s inlet bore is larger than most hydration tubes. It is more a clip connector than intended for simply squeezing into a hydration tube. I found that by pouring boiling water on the HydraPak tube to soften it and utilising a bit of brute force, the HydraPak hydration tubing will ease over the Storm Valve stem- just!

The extended drink tube cap from HydraPak weighs 20g. When the HydraPak silicon bite valve on this is changed out to the push/pull Source Storm Valve, this increases to 24g, or 28g with the Source dust cover retained.

Source Storm Valve
Source- Storm Valve
Source Storm Valve
Source Storm Valve
Dust cap on Source Storm Valve
Dust cap on Source Storm Valve
650ml filter soft flask with extended Ultraflask neck and replacement Source Storm Valve
600ml filter soft flask with extended Ultraflask neck and replacement Source Storm Valve. Total dry weight- 53g

Despite the differences in fit within the bottle holder of the three flasks, it is easy to drink from any of them while hiking with no need to pull any flask/bottle from any pocket. Drinking can be aided with the gentlest of squeezes of the flask body. For use in the Bottle Rocket the BeFree collapsible flask, with more efficient and preferable sipper valve fitted to the extended neck, provides the best fit. This supplies 750ml of water, with a well positioned Source Storm Valve push/pull nozzle. This ensemble comes in at 48g, or 53g with the dust cover retained on the sipper valve. As a reminder, my 850ml Smartwater bottle with a sports cap weighs around 35g. But the Hydrapak flask and replacement valve is far more convenient to drink from while ‘on the go’.

One or both Ultraflasks are making their way into my daypack on dayhikes when I am packing along an extra bottle of water as they don’t leak, and have the added convenience of taking up far less room in the pack when empty.

For all that, regarding my hydration system on longer hikes, experimentation continues…

Ultraflasks from HydraPak
Ultraflasks from HydraPak

5 replies »

  1. Hi Jools, Do you know if the Rocket bottle holder are compatible with the Osprey talon rucksack please.


    • Not sure Bob. Miss Three Points of the Compass has an Osprey Talon 33 from a few years back. The Bottle Rocket cannot attach to that, however newer or larger Ospreys may come better equipped. A distinct lack of fastening points


  2. Have you tried the Hydrapak “Seeker” model – seems to be a slightly different material than these you tried? I’m on my second one (returned the first in case it was a fluke) and I can NOT stomach the taste and smell. I did as they directed: add some drops of lemon juice to water and freeze overnight. If that doesn’t do it try milk in the fridge overnight… didn’t work (and I did 4 cycles of lemon, 1x of lime too, 3x of milk… that was expensive… and tried Camelbak cleaning tabs and Efferdent denture cleaner as many people use and it was STILL horrible!). I’ve owned Platypus, Evernew, CNOC, Camelbak, etc. etc. and never anywhere near as bad a taste as these Hydrapak Seeker bladders.


    • Yes I have tried the Seeker bladder. You will have noticed I mentioned it and showed the Seeker from my current hydration set-up. I do agree there is a taste. Perhaps I have become used to it over the years and miles or perhaps any overtly offensive taste has decreased over time. It doesn’t really bother me. The old iodine water treatment I used years ago was far more distasteful I found!


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

Follow Three Points of the Compass on

Enter your email address to follow this blog and receive notifications of new posts by email.

Join 285 other subscribers


%d bloggers like this: