Mountainsmith Zerk 40L Backpack

Updated for 2026!

Co-designed by Mountainsmith and Former Marine/renowned thru-hiker The Real Hiking Viking, the updated ZERK 40 pack stands alone as the ideal combination of lightweight durability, comfort, and accessibility. The Zerk contains modular features, like the compression straps and bungees, that increase the versatility of the pack on trail while allowing you to strip weight when minimalism is key. It's an all-around, thought-through pack, providing features where you want them while allowing easy customization where you don't.

Features:

• 1.5” removable hipbelt with Gatekeeper attachment hardware 
• Frameless with a removable interior frame sheet
• Roll-top closure with opposing SR buckles for self-closing roll top or for side panel attachment with removable straps
• Extra-wide shoulder straps with dual adjustable sternum straps
• 4 Large mesh front pockets on shoulder straps (2 per side) accommodate 500ml bottles, bear spray, cell phones, GPS units, etc
• Airflow EVA foam padded shoulder straps
• Modular side compression straps (removable) for securing load throughout entire pack or discarding entirely
• Customizable and removable front panel bungee system
• Large main compartment holds up to 40 liters of gear with extra 4L storage in roll-top area
• Ultra-durable Spundura stretch mesh pockets with UHMWPE grid for durability in key areas of wear
• Additional upper side panel stretch mesh pocket for quick access to items you need on the go
• Front zippered pocket for improved organization of trail valuables
• Reflective bungee and select webbing hits for increased visibility
• Dual side water bottle pockets with angled openings for easy access
• Redesigned interior pattern to accommodate 700 in³ sized bear canisters 
• Adjustable over-the-top V-shaped compression strap with SR buckle closure
• Hydration bladder sleeve with hose port (Bladder Not Included)
• Bright yellow lining promotes visibility
• Compatible with Zerk accessories 

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Specs

Volume: 44L (with fully extended collar)

• Internal volume: 40L with roll-top compressed

Weight: 

• With Accessories: 34oz | 964g
• Without Accessories: 30oz | 850g

Recommended maximum load capacity: 30lbs | 14kg

Dimensions: 12"L x 20"H x 9"D | 30.5cm x 51cm x 23cm

Sizing:

• Torso range: 16"-21" | 41cm - 53cm 
• Waistbelt: 28" - 48" | 71cm - 122cm

Materials:

• 210d Robic® Nylon X-Grid Extreema (UHMWPE) R/S UTS*
• 100d Robic® Nylon X-Grid Extreema (UHMWPE) R/S UTS*
• Spundura Stretch Mesh (w/ UHMWPE grid)*
• 150d High Density Poly Liner*
• YKK® Zipper
• EVA Foam
  

Made in Vietnam

Based in Golden, CO | Est. 1979