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Inertia 18L H2O Hydration Pack

4.8 out of 5 stars
5 Reviews
$71.47 - $109.95
Up to 35% off
Color:Obsidian Black


Size Chart


Why We Like the Inertia 18L H2O Hydration Pack

For day hikes where one water bottle won't cut it, we load up the Inertia 18L H2O Hydration Pack to stay equipped for a long day on the trail. The included reservoir stays secure in its dedicated zipper pocket, and the inline hose conveniently detaches for easy refills that don't require us to remove the hose from its shoulder harness.


  • Hydration pack holds the essentials for long day hikes
  • Sturdy nylon is lightweight and resists trail wear
  • DWR treatment sheds light rain to protect contents
  • Includes 2L quick-drying reservoir for ample hydration
  • 3D multi-density foam backpanel for a comfortable carry
  • Removable hipbelt offers more support if needed
  • External zipper pockets keep the essentials at hand
  • Item #GREZ084
Responsible Collection
Bluesign Approved, Recycled/Repurposed
[face fabric] 210D HD nylon, 420D HD nylon, PFC-free DWR coating, [lining] 135D polyester, PFC-free DWR coating
18L (1098cu in)
3D foam back panel
Shoulder Straps
multi-density foam
Waist Belt
Hydration Compatible
Reservoir Included
2L 3D Hydro Reservoir
front panel
1 zippered top, 1 zippered side, 2 side mesh
Trekking Pole Carry
Weight Capacity
[packed] 19.3 x 9.8 x 7.5in
Claimed Weight
1lb 3.5oz
Manufacturer Warranty
limited lifetime

Overall Rating

5 based on 5 ratings

Review Summary

1 Stars - 0 reviews
2 Stars - 0 reviews
3 Stars - 0 reviews
4 Stars - 1 reviews
5 Stars - 4 reviews

What do you think about this product?


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5 out of 5 stars

January 22, 2024

Perfect day trip pack

I love this pack for day trips, both hiking and snowshoe. The bladder is easy to access, fill, and secure. The main compartment has sufficient space for a first aid kit, food, wind/water proof shell with room to spare. I only wish that it had a better means to secure snow shoes for hikes where they are not initially needed.

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Neil S

Originally reviewed on

5 out of 5 stars

August 22, 2023

Awesome Day Pack

This is a fantastic and comfortable day pack. I have used it on a few hikes and it has been awesome. The mesh panel helps with breathability, but if you run hot you’ll still sweat with this pack. I love the separate hydration sleeve and the clip that keeps the hydration pack steady. The hydration pack it comes with is amazing and easy to clean. The only think that could make it better would be a rain cover to go with the pack.

Aaron W

Originally reviewed on

4 out of 5 stars

May 14, 2023

Would love it, if…

I like the fact that this pack has three outer mesh pockets, one 3L water reservoir compartment including hose routing straps, and a comfy breathable meshed back support plus shoulder straps. I WOULD LOVE this pack if it had one additional inner pocket for keeping valuable electronics and wallet away from easy reach and thieves. I WOULD ALSO LOVE this pack if it had a single-handed, quick-pull draw cord with a weather flap seal in order to access the MAIN COMPARTMENT without the use of a cumbersome zipper, which slows me down when in outdoor conditions. Other than that, this pack is beautifully made.


Originally reviewed on Gregory

5 out of 5 stars

April 3, 2023

Outstanding Quality

This H2O backpack is awesome in every aspect. Quality materials, great fit and many options.

Mark S

Originally reviewed on

5 out of 5 stars

May 27, 2022

Absolutely Perfect Bag for Day Hikes + Hydration

[This review was collected as part of a promotion.] I did receive this pack as a #giftedproduct, but that in no way influences my review or remarks. I have been a huge fan of Gregory for years. I use their bags for backpacking, day hikes, and commuting. Their bags are top-notch quality, feature-rich and comfortable. The Inertia 18 is no exception. Why do I love it? The small footprint gives way to a massive amount of capacity without feeling too bulgy. The bag itself has a shape that it doesn't lose when empty - making it easy to pack up, sort through, and clean up. It's got all the bells and whistles that can be jammed into a small package: Amply sized main storage compartment, a separate hydration pocket, a front knickknack pocket at the top, a mesh water bottle side pocket, and a bonus zip pocket on the other side. The back panel mesh on the back allows pretty good airflow, and the straps are nice and lightweight so they don't feel too bulky or heavy - even when the sweat hits. But the gem: The hydration system. Gregory absolutely killed the game with their hydration systems - hands-down best on the market. This bag comes with a 2L bladder which is the perfect size for most hikes that I do. On hot days, I will throw an iced-down water bottle in the side pocket. (I Live in AZ). The bladder has a quick release system meaning you can completely pull it out to fill it up. So easy and clean. It has a wide mouth to make filling simple. There is a handle to help carry the bladder outside of the bag. The lid twists on and off with ease and is very secure - which is where many other brands go amiss. The INertia's hydration compartment has a built-in hook to hang the bag from so it doesn't slump around, and because of the hardened back panel of the bladder, it stays in place - and keeps that water upright and ready to flow. It's also the simplest water hydration system to clean. Gregory integrated a hook for you to be able to hang the bladder upside down. I usually throw a paper towel or small towel in the bottom to soak up any water, making sure to keep the mouth open for airflow while the bladder dries itself out.

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Originally reviewed on Gregory