Mountainsmith Zerk Ultralight 25L Hiking Backpack — Cyan Blue

Meet the Mountainsmith Zerk Ultralight 25L

The Zerk 25L is built for hikers who value weight savings without sacrificing essential capacity. At 1.7 lbs when empty and compact at 20” x 12” x 9”, it aims to keep you moving with up to 20 lbs of load while staying close to your back. Its 23-liter main compartment, plus smart storage pockets, helps you organize gear for quick access on the move. The large side water bottle pockets with angled openings are designed for one-handed reach, while the expansive front mesh pocket invites bulky items to ride along without crowding the core space.

Why it fits thru-hikes and day adventures

Crafted with the realities of long days on the trail in mind, the Zerk 25L balances weight, durability, and accessibility. Reflective screen printing and cord loops improve visibility in low light, and the front cord loops can be configured with the included bungee cord for adaptable carry options. The lid closure with side compression SR buckles and a front SR buckle closure provide reliable securing points that stay put as you move.

Storage and organization

• Large main compartment holds up to 23 liters of gear for a compact, efficient packing setup.
• Side water bottle pockets with angled openings enable easy removal and insertion while walking.
• Expansive front mesh pocket is ideal for bulky items like a jacket or layers you grab frequently.
• Large mesh side stash pockets offer quick access to small essentials without slowing you down.
• Reflective details and cord loops enhance visibility and customization for low-light runs or early starts.

Comfort, fit, and durability

• 1.5” removable waistbelt and adjustable torso range (16"–19") support a personalized fit and stability.
• Side compression straps help secure the load along the torso for better balance on uneven terrain.
• Removable interior laser-cut frame sheet (EVA Atilon) adds stiffness for shape retention and airflow behind the pack.
• Co-designed with The Real Hiking Viking, the Zerk 25 aims to merge weight savings with practical features and proven durability.

On the trail

Expect a nimble option for ultralight hikers, quick day trips, or adventurous overnighters where every ounce counts. The layout supports a simple, efficient workflow: grab essentials from accessible pockets, adjust the fit on the fly, and move with a balanced, comfortable carry. It’s a practical companion for hikers who value a streamlined setup with room to grow into longer adventures.

Quality you can count on

Mountainsmith packs are known for durability and thoughtful design. The Zerk 25L embodies that philosophy with a layout designed for reliability, everyday rugged use, and long-term performance on the trail. While outcomes depend on your pace and terrain, the combination of light weight, organized storage, and adjustable fit makes it a credible option for hikers seeking efficiency and comfort.