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Moving fast with an ultralight load? Enjoy your time on the trail with the Mountainsmith Zerk 40 pack, which was designed with renowned thru-hiker and triple-crowner The Real Hiking Viking.


  • Development with The Real Hiking Viking—including countless hours, a hundred beers and one giant beard—resulted in a pack that can withstand thousands of miles of use per year
  • Ultra-running inspired shoulder straps are extra wide and padded with EVA foam for comfort and stability
  • 4 large mesh front pockets on the shoulder straps (2 per side) offer easy access to small essentials
  • Adjustable sternum strap includes a safety whistle
  • 1.5 in. removable hipbelt is there when you want it, gone when you don't
  • Removable, laser-cut EVA Atilon framesheet on the interior allows for rigidity and airflow
  • Large main compartment holds up to 40 liters of gear
  • Roll-top closure with opposing side-release buckles gives you multiple closing options
  • Removable, over-top webbing straps with side-release buckles secure a sleeping pad, bear canister or other accessory
  • Side compression straps secure the load throughout the entire pack
  • Expansive mesh pocket on front hauls bulky gear
  • Large water-bottle and mesh stash pockets on the sides feature angled openings that let you easily remove and insert items while on the go
  • Front cord loops can be configured with included bungee cord
  • Front panel bungee attachment system
  • Reflective screen printing and cord loops for low light visibility


View all Mountainsmith Backpacking Packs

Technical Specs

Item #203418
Best Use


Frame Type




Gear Capacity (L)

40 liters

Gear Capacity (cu. in.)

2,440 cubic inches


1 lb. 14 oz.

Fits Torso Length (in.)

16-19 inches

Fits Waist/Hips

28-48 inches


210-denier EXTREEMA recycled nylon ripstop (UHMPE); recycled 210-denier nylon SD oxford; nylon 100-denier x Span 840-denier stretch mesh

Number of Stays


Reservoir Compatible


Pack Access


Number of Exterior Pockets

9 + main compartment


18.5 x 11.75 x 5.75 inches



2 reviews with an average rating of 5.0 out of 5 stars

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