Guest Gear Review: Gu 5 Serving Hydropak Flask

Things have been a bit quiet over here at Duffrunning Towers lately because of a post London marathon niggle/injury/pain related situation I’m dealing with, which means there is very little running happening and therefore not a lot to write about. I might do an update about the whole sorry saga at some stage if I can make it sound less dreary and dull than it is in real life.

In the meantime here’s a review of a piece of gear we found at the London Marathon Expo, written by my friend Jenny who is running and has therefore been able to try hers out!

Jenny has had a great year for running so far, completing both the Boston and London marathons and earning a place in our club team for the prestigious Welsh Castles Relay. She’s also due to tackle her second ultra very soon, all of which makes her very qualified to review a piece of nutrition gear.

Here’s what she thought of Gu’s 5 Serving Hydrapak Flask:

Flying at the Welsh Castles Relay

Way back in April, when Angela and I went to the London Marathon Expo together, we spent rather a lot of time at the Gu stand.  We were seduced by the enormous array of tempting flavours on offer, and the nice chap trying to sell them let us taste about ten different options each.  We came away feeling very much like the tops of our heads were going to fly off through over-exposure to sugar and caffeine, but also each clutching Gu’s new 5-serving reusable flask.  They’ve made this to go alongside their 15 serving gel pouches, which at £20 for 15 servings are better value than the usual £43.20 for a box of 24 gel packets.  The flask costs £17, so by my calculations you recoup its costs after roughly 36 gels.  That sounds like a season’s worth of marathon training to me!  Gu don’t offer their full range of flavours in the 15 serving pouch (I also have a box of birthday cake flavoured individual gels!) but there are definitely enough options to cater to all tastes.  I chose vanilla.

The Gu 5 serving flask and a bulk pack of one of the fruity flavour gels

I was intrigued by the non-sticky promise of the flask, and also liked the idea of producing less waste than the individual gel packets.  I got the chance to try it out for the first time on my big birthday run (23.5 miles to a pub for Angela’s excellent cupcakes!), so here are my thoughts on its performance pre, during and post run.


Before – I was curious as to how easy it would be to fill up.  Turns out very; the pouch pours easily, and the neck of the flask is wide.  It was initially a bit tricky to hold both and pour at the same time, but once I treated it like an icing bag and propped it up inside a glass, it was absolutely fine.  The pouch has markers so that you can tell how many servings you’re putting in.

During – It was incredibly easy to use on the run.  The nozzle is specially designed to be wide enough for the quite sticky gel to flow through, and I got the hang of twisting it open and closed with my teeth, so you don’t even have to touch the nozzle.  I was storing it in the side pocket of my inov8 ultra pack, but it would have been comfortable to hold in hand if you weren’t wearing a bag.  It probably wouldn’t fit easily into a pocket, though.  I also liked being able to have gel little and often, rather than needing to take a whole one in one go or have to carry the packet along with me.  It was obviously great not to finish with a pocketful of sticky gel packets!  I got on ok with the gel itself – Gu is a bit heavier than other options, with packets holding 30ml rather than the 60ml of my normal Science in Sport.  I found that the first mouthful hit my stomach a bit heavily, but after that it was fine.  The flavour is great if you like excessively sweet things!  They have options for different amounts of caffeine ranging from zero to rocket fuel.

After – My biggest concern about the flask was how easy it would be to keep any unused gel, as I didn’t want to save money up front only to end up throwing half a flask away if I didn’t use it.  I made the error on the homeward journey of putting the flask inside my bag, where the nozzle twisted slightly and leaked onto the other contents.  Thankfully I’d been organised and dry-bagged everything, so clean-up was not too problematic.  I also discovered that with a little patience, it was possible to squeeze the leftover gel back into the original pouch, although this was fiddly, and would be easier if the gel pouch had a wider nozzle.  I’m not sure how I’ll feel about doing this every week!  The pouch was then very easy to wash clean; all of the remaining gel came out easily with a short soak in hot water.


Does what it claims? 10/10 – performs exactly as we were told it would, and the gel is tasty, as well as delivering the quick but sustained energy hit you need.

Useful for runners? 8/10 – probably only useful to you if you are regularly marathon or ultra training, and carry a bag/vest to do so.  I don’t see it being so useful for someone who typically stores things in pockets, as it’s a bit big for that.

Value for money? 7/10 – the Gu gel is pretty expensive compared to other brands, but the flask does improve things.  I have used Science in Sport gels for the past few years, which if bought at the right time in their sale can come in at less than £1 a gel; better value than the Gu.  Having said that, I am using less gel by being able to take sips when I want it, so maybe overall it will be better value!

Final Thoughts – I’m definitely glad I’ve got it, and I will use it again.  It will be particularly useful for ultra races, when I want a steady supply of gel little and often, and have the pack to store it in while running.  For marathon racing, I think I will probably stick to packets, as I won’t want to carry the flask for the entire race.  If you don’t mind a bit of faffing before and after for the sake of saving a little waste and not carrying your sticky gel packets, it’s a good investment.

You can check out the details of the flask and a video showing how to use it on Gu’s website here.

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