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  • Hydration system features a 3-liter (100 fl. oz.) reservoir that conforms to your back's shape even when full, resulting in a precise, stable and comfortable fit
  • Rigid spine / handle stabilizes the reservoir, making it easy to slide it into its dedicated compartment; large mouth makes filling and cleaning easy
  • Back panel features ridge-molded foam with channels covered in mesh to allow airflow
  • Contoured shoulder straps have breathable mesh and perforated foam; stretch-mesh pocket and zip media pocket keep items close
  • Webbing waistbelt helps stabilize pack during demanding descents
  • Zipper around back panel lets you access the main compartment without removing gear from the front
  • Quickly attach a helmet with the adjustable LidLock™ helmet clip
  • Padded front compression pocket secures a full-face helmet; body armor fits in the side mesh pockets or behind compression pocket
  • Top zippered pocket is lined with a soft fabric that helps keep sunglasses, goggles or other fragile items from getting scratched
  • Pack includes a removable tool roll, which has its own zip pocket at bottom of pack
  • Compression straps let you cinch down loads for jostle-free carrying
  • Reflective hits increase visibility in low light


View all Osprey Cycling Hydration Backpacks

REI membership


Best Use Mountain Biking
Frame Type Internal Frame
BPA Free Yes
Gear Capacity (L)
15 liters
13 liters
Gear Capacity (cu. in.)
915 cubic inches
793 cubic inches
Reservoir Capacity (fl. oz) 100
1 lb. 14 oz. ounces
1 lb. 13 oz. ounces
Adjustable Torso Yes
Fits Torso 15 - 21 inches
Fits Waist/Hips 38 - 53 inches
Material(s) 330-denier nylon/420-denier nylon
Pack Access Panel
Number of Exterior Pockets 5
Bite Valve Shut-Off Switch Yes
Wide-Mouth Opening Yes
Dimensions 13 x 9 x 9 inches
Gender Unisex
Rated 5 out of 5 by from Excellent pack!!! This pack is great in my profession. I am an Archaeologist and I work in what is called Cultural Resource Management, we conduct archaeological surveys prior to construction of anything that may impact the environment and any documented or undocumented archaeological sites. My job requires a lot of back country hiking that this pack allows me to succeed at. The size is perfect for hiking through tight vegetation, the weight is light and the build is comfortable. So comfortable I forget it is on! And the ease of access allows me to retrieve my equipment with speed, and it is easy to manage as I am definitely a minimalist when it comes to such. Well done and thanks Osprey!
Date published: 2017-01-08
Rated 5 out of 5 by from Great Product I used to have a camelbak for biking, but found it was too small. The Zealot has an opening on the back that can be used for a Full-Face Helmet or other things, side pockets, a stash pouch on the top for valuables, and a tool pouch on the bottom that is super convenient (comes with tool roll) the pocket for the reservoir goes the whole length of the bag so that when you open it, the whole back of the bag folds down. You can fit a bladder, jacket/layers, first aid kit and lunch in this pocket as well. There are also hip pouches that are good for a multi tool or leatherman, and two chest pockets on the straps that don't fit much. As always, you have amazing Osprey fit and finish, and it seems that the fabric is durable enough to take a spill on (though I have not tested that yet).
Date published: 2016-05-09
  • y_2017, m_5, d_25, h_10
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Does the waist size 38 - 53 also apply to the s/m pack? I'm a 33 inch waist size.

Asked by: UPS Guy
The waist and torso size is the same on the S/M and the M/L pack. The only difference in sizing is the S/M pack is 13 liters while the M/L pack is 15 liters.
Answered by: REIservice
Date published: 2016-08-16

Can you buy a second tool roll for if you want one for bike tools and the other for hiking gear and be able to swap them as needed?

Asked by: Brian
The removable tool roll is manufactured for this pack only and is not available as a separate accessory.
Answered by: REIservice
Date published: 2017-04-27

will this be a good fit for a 29 waist 

Asked by: kait
​The S/M pack is a good fit for your waist.
Answered by: REIservice
Date published: 2017-03-16

what is the difference between this zealot 15 and the zealot 15 from the rei garage?

Asked by: kallie
They are the same pack except for the reservoir itself. This one has the newest reservoir design from Osprey with a slide seal closure, whereas the one on REI Garage has a reservoir with a screw top closure.
Answered by: REIservice
Date published: 2016-12-16
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