The Mountainsmith Zerk 25 is a backpack with vest-style shoulder straps for day hiking and fastpacking. Numerous open mesh pockets on the shoulder straps and backpack exterior make it easy to store frequently accessed gear and food, so you don’t have to stop and open the pack to access them. While it’s similar to the higher-volume Mountainsmith Zerk 40, several notable differences exist. The Zerk 25 has a top lid pocket instead of the roll-top closure on the Zerk 40; it has two front sternum straps instead of one, and is entirely frameless without additional back panel padding.
RELATED: 10 Best Hiking Daypacks
- Weight: 1 lb 7.5 oz (666g)
- Volume: 25L
- Type: Frameless
- Access: Top
- Gender: Unisex
- Hydration compatible: Yes, center port
- Pockets: 11 (2 closed)
- Detachable hip belt: Yes
- Torso Range: 16-24″
- Includes extras: Stretch bungee cord for the front pocket
- Materials: 210-denier recycled Robic nylon ripstop (UHMPE)
- Max recommended load: 20-25 lbs
- Pros: Numerous and highly functional pockets, comfortable vest straps
- Cons: Shoulder straps are too long for shorter torso lengths, carries best when mostly full
Backpack Suspension
The Mountainsmith Zerk 25 is a frameless, top-loading daypack/fastpack with vest-style shoulder straps, numerous external and closed pockets, and an optionally removable hipbelt made with a wide webbing belt with a solid center buckle. Being frameless, the purpose of the hip belt is to keep the pack from bouncing when running or hiking. Depending on your torso length, it will loop around your hips or higher up on your torso: it doesn’t really matter which since the weight of the pack rests entirely on your shoulders and upper chest.
Each shoulder strap has two stacked mesh pockets on the front with tensioners and gear loops along the side so you can secure items like an inReach Mini 2 to prevent it from getting lost even if it falls out of a pocket. The pockets are large enough to securely store a smartphone or a 500 ml soft bottle with ease and really make the pack convenient to use. They are the best pockets I’ve found on any fastpack all year, and I’ve tested nearly a dozen, including the Osprey Talon Velocity 30, Gossamer Gear Fast Kumo 36, and the Outdoor Vitals Skyline 30, to name a few.
While the Zerk’s shoulder straps aren’t heavily padded, they’re also not gossamer thin. They’re 3″ wide at the top and sewn directly into the top of the pack bag, widening to 4.5″ at the bottom, with two sliding sternum straps between them. The straps themselves are J-shaped, which may be a consideration if you’re female or have a well-developed chest where S-shaped straps would be more comfortable. The jury is still out on whether women find fast-pack shoulder straps and sternum straps comfortable or not.
Backpack Storage and Organization
Except for its top lid pocket, the Zerk 25 is laid out like a typical ultralight pack with a roll-top, front mesh pocket, and side water bottle pockets. The top lid has two zippered pockets: a large pocket on top with a key fob and a mesh pocket underneath the lid. I prefer having a top lid or clamshell opening on a daypack over a roll-top because I access the contents of my pack more frequently than when I’m backpacking, and my only goal is to crush miles all day. Trying to find items packed in a roll top is a pain in the butt since you often have to remove everything and repack it again. That gets old fast.
There’s a front stretch mesh pocket, which is good for holding loose layers like rain gear, your lunch, or a wet water filter. It has a top webbing strap to hold it shut and keep contents from falling out. There are also two stacked pockets on each side of the Zerk: the inner one is solid fabric with an elastic tensioner on top, while the outer pocket is made with stretch mesh, which I liken to “hamster cheeks. These are good for storing extra snacks, fruit, or even trash wrappers so you don’t have to stop and open your pack to access/stow them. I much prefer these “hamster cheek” pockets to the mesh pockets that many ultralight backpack makers have started putting on the base of their backpacks. The latter makes no sense from a durability perspective since the highest abrasion on a pack occurs on the bottom when you put it on the ground.
The rest of the Zerk 25 is fairly conventional. The pack is hydration-compatible with a center hose port between the shoulder straps, hose keeper loops on both shoulder straps, and a hook inside to hang your bladder and a hydration pocket.
Backpack Compression and Attachment Points
The Zerk 25 has a single tier of side compression straps that are good for holding longer items against the side of the pack, like a Smartwater bottle with a Sawyer Squeeze filter on top. But they don’t provide very good compression unless the main compartment is tightly stuffed because the ends are sewn to fabric and not a rigid structural support like a frame. Still, they’re quite useful when carrying longer objects like a Tenkara fishing rod.
There’s a webbing strap that loops over the drawstring closure at the top of the pack bag to provide top-down compression. Daisy chains surround the external mesh pockets and provide a convenient place to clip items like a hat or microspikes with a ‘biner. The pack also comes with an elastic bungie cord that you can loop across the side daisy chains if you want to hang wet clothing on the outside of the pack to dry. Finally, there are two ice axe loops, that could also be used to strap trekking poles to the pack using the side compression straps to hold the shafts.
Recommendation
The Mountainsmith Zerk 25 is a multi-purpose daypack/fastpack with a vest-style shoulder harness and a non-load-bearing hip belt. It is remarkably comfortable and has a plethora of pockets that make it easy to organize and access your gear on the move. There is also plenty of secure closed storage to carry extra clothing and equipment. While switching from a conventional daypack to one with vest-style straps and storage takes some getting used to, I think you’ll find that the hybrid combination of daypack and fastpack features on the Mountainsmith Zerk 25 makes this pack a keeper for adventures near and far.
SectionHiker is reader-supported. We only make money if you purchase a product through our affiliate links. Help us continue to test and write unsponsored and independent gear reviews, beginner FAQs, and free hiking guides.
