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Platypus Big Zip SL

rated 4.0 of 5 stars

The Big Zip SL has been discontinued. It was replaced by the Platypus Big Zip EVO.

photo: Platypus Big Zip SL hydration reservoir

Originally purchased as a backup, this has become my favorite hydration option. Easy to fill. I like the bite valve on this a fair bit better than the leading competitor. Clear plastic body leaves no doubt about what is inside. Heavy-gauge plastic seems built for the duration.


  • Great bite valve
  • Swivel interface between hose and reservoir
  • Clear plastic reservoir — easier to see and heavier gauge
  • Secure opening and handle are advantages


  • Heavier than most
  • Narrow opening requires brush for cleaning

Having encountered some issues with a competing hydration reservoir, i turned to Platypus as an alternative.  It became my favorite. I logged 40-50 hours of trail time with the Big Zip over the summer, mostly day hiking in hot, humid mid-Atlantic weather. It performed as one would want and expect. It didn't leak, it was easy to use, and nothing broke or failed or malfunctioned.  


Note the top handle. It is relatively easy to hold and can attach to loops at the top of a backpack if you prefer to 'hang' your reservoir. The thin top handle is flexible, which I think is an advantage.  i have broken the hard plastic 'hang tabs' on a competing product. The handle is part of a hard plastic top piece that keeps the reservoir closed. I like the extra security of having that hard plastic slider.  I will try to illustrate how it works.

As you can see, the way you fill the Platypus is via the top, which is a heavy-gauge ziplock closure. Anyone who has used a ziplock bag knows that they can 'blow open' under pressure.  


Platypus attacked this challenge by adding a hard plastic slider that keeps the zipper closed.  The slider is attached to the reservoir via a small black elastic.  Filling the reservoir, you can let the slider dangle without dropping and losing it.  That said, having a piece of plastic dangling which you fill the bag can be a little annoying.  The zipper opening is very firm — much more than any freezer bag.  Because the opening is firm and fairly small, you would need to have child-sized hands to clean the interior of the reservoir.  I cleaned it a few times using a small bottle brush.  


Once the reservoir is full, you slide the blue piece across, locking the bag shut.  It works well.  I used this reservoir about 75% of the time on my hikes this summer, and it never opened accidentally.  The downside of this assembly is that it weighs a little more than competing products i have used.  


The Big Zip SL holds 100 ounces of water - 3 liters.  The bag has a helpful measuring guide on the side to show how full it is.  You will note that with the reservoir stuffed into a sleeve or pack lid repeatedly over the past 3-4 months, some of the blue print has already worn off the bag, so it remains to be seen what will happen after 5 years.  In my view, the bag itself is one of the big advantages for Platypus.  

I like that it is clear plastic, so i can see what is inside, especially if I am drawing water from sources of the less clean and clear variety.  I also like the heavy feel of the plastic because it feels like it will last a long time and helps inhibit 'sloshing' — that feeling that the water in the bladder is moving around while you walk.  

A competing product that uses a softer plastic has resorted to inserting a baffle in the bag to limit sloshing; it's simply not an issue here.  To be fair, all the hydration reservoirs I have used have been extremely durable.  I have been using reservoirs for years and have never had a bag fail on any brand.  

Another nice feature is the hose attachment to the bag.  It swivels so the hose can extend in any direction easily.  The joint itself is fuss-free and did not leak all summer.  I was very happy about that, because a slow hose joint leak was a significant issue I encountered with another reservoir I have.  I like having the swivel because one of my backpacks holds the reservoir in the lid, so the hose tends to be at a different angle than in a hydration sleeve.  



The hose attachment can detach from the bag.  So far, I haven't done that.  

Finally, perhaps the most important part of the process - how you get water out of this.  Platypus has a fairly big bite valve that is larger than others i have used.  It took me a little time to get used to it - you really have to bite the edge of the valve.  Water flow is very good, and the valve has not leaked or developed any drips, which is an issue than can develop with hydration bite valves.  The bite valve has a built-in twist valve to shut off water flow - important if you tend to toss your pack into a trunk without thinking whether the pack is pinching the bite valve.  With one competing brand, I had to purchase a separate shut-off valve.  


I also like that Platypus includes a clip to attach the hydration hose to your shoulder strap; with some other brands, I have had to purchase loops of velcro or other extras so the hose doesn't hang loose.  


Overall, the Platypus Big Zip is a thoughtfully designed and well-executed hydration system. I have been very pleased with it.

Source: bought it new
Price Paid: $35

Worth the switch! After long time dedication to a competitor, no regrets; Nice construction, long tube, and a well engineered sure close system.


  • Good construction
  • Odor free
  • Ample tube length


  • Narrow mouth for filling

I recently upgraded to this 100oz. reservoir in preparation for an Appalachian Trail section hike. The capacity does a great job with a water bottle to get through dry areas. I wasn't initially impressed, however after going on its maiden voyage, I have completely changed my mind...

It is a very easy to use system, and the quick disconnect is a big plus for refilling without having to pull the hose. I also like the 180 degree swivel action at the disconnect. I thought that the bite valve was a little large, however after several uses now, I don't mind it at all. I find the shutoff valve to work without fault. There is a removable, adjustable clip which also adds to the ease of adjustment.



The reservoir has clear markings, and is made of high quality BPA free plastic. It may be a little difficult getting a scrubber in to clean, but the four I've owned all have this concern. The opening has a zip-lock type opening, with a plastic retainer that slides on.



Another engineering plus is the elastic lanyard that keeps you from dropping, or misplacing it, along with a handle for hanging. 

This unit is still 100% over its short life (<3 months), but I anticipate it to last 10 years + with good care.

Source: bought it new
Price Paid: $35

Worked well enough, however I found better options in my thru-hike of the Appalachian Trail in 2012.


  • Durable bladder
  • Zip top is awesome


  • Developed leak at hose connection
  • Bite valve gets really dirty unless you purchase valve cover

I started out with this at Springer, but sent it home in favor of just carrying two Powerade bottles by Pearisburg. Now, I wouldn’t have thought about making that switch if it wasn’t for an unfortunate leak that somehow developed where the hose attached to the bladder when I was in Virginia. Luckily I purchased it at REI and so I was able to return it later.

Really at the time I figured I would use Powerade bottles just for a few weeks or until I could get it exchanged, but after the first few days I didn’t even bother. I absolutely hated having to stop for water, pull out the bladder from the sleeve inside my pack, fill it up and then attempt to fit it back in the pack which usually resulted in me having to entirely repack everything because it was kind of bulky.

I also found that because I was fearing having to go through this process, that I wasn’t drinking as much water as I should have. With two Powerade bottles, I could simply chug all 2L of my water, then refill them both without much bother and be on my way. Plus, after maybe three weeks of using the same Powerade bottles, I would throw them away in town and then purchase two brand new Powerades. You get tired of drinking plain water, so this was very welcome.

I discovered later that you can actually get a connection at the bite valve which allows you to pump straight from your filter into the bladder without having to remove it from the pack, which is awesome. If I’d had that I might have actually stayed with this system.

In the end though, I’m glad I dropped the Platypus for my thru-hike, but also realized that I might actually still use it for future day-hikes. Super lightweight plastic Powerade bottles are just much simpler.

Source: bought it new
Price Paid: $35

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Price MSRP: $32.95
Historic Range: $18.83-$34.95
Reviewers Paid: $35.00

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