Mountainsmith Zerk 40 vs Mountainsmith Zerk 20 UL Daypack
Quick take: The Mountainsmith Zerk 20 UL Daypack costs $50.05 less; the Mountainsmith Zerk 40 carries more (40 vs 20 liters); the Mountainsmith Zerk 20 UL Daypack is lighter (1.75 vs 2.13 lbs).
Which one to buy
Day hikes or nights out? These two Mountainsmith Zerks share the same tough Robic Extreema grid fabric and a removable frame sheet, but they're built for different trips. The Mountainsmith Zerk 20 UL Daypack holds 20 L, or 23 L with the top extended. It's rated for a suggested 20 lb, or 30 lb when pushed, and weighs 1 lb 6 oz stripped. The Mountainsmith Zerk 40 is the overnight pack. Mountainsmith lists 40 L (44 L extended) and one review measured about 51 L. Mountainsmith suggests 30 lb, up to 45 lb, though reviewers find it most comfortable around 20-25 lb.
Fit and the hipbelt separate them as well. The Zerk 20 suits 15-19 in torsos, so taller hikers may find it short, and its belt is a removable 1.5 in webbing strap with no pockets. The Zerk 40 covers 16-21 in torsos and includes hipbelt pockets. It also lets you run with or without the frame sheet as your base weight drops. Neither is waterproof, so the 40 calls for a liner, though its woven fabric takes trailside tape repairs well. Bear canisters ride vertically inside the 40; reviewers advise against the top canister straps. If your trips include nights out, the 40 is the one to buy, and a separate daypack can come later.
Mountainsmith Zerk 40
For overnight and multi-day hikers who want one pack that runs framed or frameless, with hipbelt pockets and more room than its label suggests.
Mountainsmith Zerk 20 UL Daypack
A good match for day hikers who carry a lot of water and layers and want a frame sheet in a 20 L pack, as long as their torso is 19 in or shorter.
| Spec | Mountainsmith Zerk 40 | Mountainsmith Zerk 20 UL Daypack |
|---|---|---|
| Price | $230 | $179.95 |
| Rating | — | — |
| Type | Ultralight Pack | Daypack |
| Frame Type | Internal Frame | Internal Frame |
| Capacity | 40 L | 20 L |
| Weight | 2.13 lbs | 1.75 lbs |
| Max Load | 30 lbs suggested (up to 45 lbs) | 20 lbs suggested (30 lbs for demanding use) |
| Torso Fit | One size, 16-21 in torso | 15-19 in; waistbelt 28-48 in |
| Material | Robic nylon X-Grid Extreema ripstop with UTS coating | 100D/210D Robic nylon X-Grid Extreema (UHMWPE) ripstop with UTS coating, high-density poly liner |
| Back Panel | Removable frame sheet | Airflow EVA foam over a removable EVA/Atilon frame sheet |
| Adjustable torso | No | No |
| Ventilated back | No | No |
| Raincover included | No | No |
| Hipbelt pockets | Yes | No |
| Removable lid | No | No |
| Hydration sleeve | Yes | Yes |
| Fits BV500 bear can | Yes | No |
| Warranty | Mountainsmith lifetime warranty against material and workmanship defects; repair or replacement at Mountainsmith's discretion | Mountainsmith lifetime warranty against material and workmanship defects; repair or replacement at Mountainsmith's discretion |
Pros & cons
Mountainsmith Zerk 40
- ✓The removable frame sheet means one pack covers both framed and frameless use.
- ✓One review measured about 51 L against the 40 L badge, where most packs here measure under.
- ✓Robic X-Grid Extreema ripstop (100D body, 210D base and back) is a tough woven fabric that repairs easily.
- ✓$230 is mid-range for the segment and below most cottage packs of similar volume.
- ✓Mountainsmith is a mainstream brand, so returns and support are simpler than cottage brands'.
- ✓1 lb 14 oz stripped (2 lb 2 oz full) is competitive with dedicated ultralight packs.
- ✓Hipbelt pockets included.
- ✓Widely available rather than made to order.
- ✗A removable frame sheet is less effective at load transfer than stays or a hoop.
- ✗No adjustable torso.
- ✗Not waterproof, unlike the laminate packs at this price.
- ✗Mountainsmith has less ultralight credibility than the cottage brands it competes with.
- ✗The 40 L badge understates the pack, which makes cross-shopping confusing.
- ✗Fewer configuration options than a made-to-order pack.
- ✗Limited presence on long trails, so fewer real-world reports.
Mountainsmith Zerk 20 UL Daypack
- ✓A removable frame sheet in a 20 L daypack lets it carry up to a suggested 20 lb, or 30 lb when pushed.
- ✓UHMWPE-grid Robic body with a poly liner is more abrasion-resistant than typical recycled-polyester daypacks.
- ✓It drops to 1 lb 6 oz with the frame sheet and belt removed.
- ✓Hydration sleeve included, and YKK zippers throughout.
- ✗$179.95 is high for a 20 L daypack; mainstream framed daypacks of this size often cost $100-150.
- ✗The waistbelt is a removable 1.5 in webbing strap with no pockets.
- ✗One torso range (15-19 in) only, so taller hikers may find it short.
- ✗No raincover or ventilated back.
Mountainsmith Zerk 40 vs Mountainsmith Zerk 20 UL Daypack: common questions
Can the Mountainsmith Zerk 20 UL handle an overnight trip instead of the Zerk 40?▾
Only a very minimal one. At 20 L, or 23 L extended, it's built as a daypack. The Zerk 40 lists 40 L, one review measured about 51 L, and it is the one designed to hold a sleep system, food and a canister.
Which Zerk fits a taller hiker?▾
The Zerk 40, which covers 16-21 in torsos. The Zerk 20 UL fits 15-19 in torsos, so hikers above that range will likely find it short.
Do the Zerk 40 and Zerk 20 UL have the same frame?▾
Both use a removable frame sheet, so either can be stripped down. The Zerk 20's is EVA and Atilon under Airflow EVA foam and is suggested for 20 lb. Mountainsmith suggests 30 lb for the Zerk 40, though reviewers find it most comfortable around 20-25 lb.