Kapten & Son Fyn 13L vs Mountainsmith Zerk 13 UL Daypack
The Kapten & Son Fyn 13L is 13L and 0.8kg1.8lb; the Mountainsmith Zerk 13 UL Daypack is 13L and 0.82kg1.8lb. The Kapten & Son Fyn 13L is 0.02kg0lb lighter. The Kapten & Son Fyn 13L fits the carry-on limit of 36 of 36 major airlines and the Mountainsmith Zerk 13 UL Daypack fits 36; under the seat, 20 and 1 of 26.
| Spec | Kapten & Son Fyn 13L | Mountainsmith Zerk 13 UL Daypack |
|---|---|---|
| Price | n/a | $164.95 |
| Volume | 13L | 13L |
| Weight | 0.8kg1.8lbBest | 0.82kg1.8lb |
| Carry-on compliance | 100% | 100% |
| Personal-item compliance | 77%Best | 4% |
| Dimensions | 39.5×28.5×12.5cm15.5×11×5in | 45.7×22.9×12.7cm18×9×5in |
| Laptop | 15.6" | no laptop sleeve |
| Bottle pockets | n/a | 2 |
| Opening | Velcro | Panel access, Panel loader main compartment |
| Warranty | n/a | Lifetime |
| Torso length | n/a | 38.1 to 48.3cm (15 to 19in) |
| Organizer | Yes | Yes |
| Shoe compartment | No | No |
| Hydration sleeve | No | Yes |
| Frame sheet | No | Yes |
| Water-resistant | Yes | No |
| Rain cover | No | No |
| MOLLE | No | No |
| Hip belt | No | Yes |
| Sternum strap | No | Yes |
| Load lifters | No | No |
| Shoulder strap | No | No |
| Luggage pass-through | Yes | No |
| Camera compartment | No | No |
| Material | 75% recycled PET, 15% PU, 10% polyester | 100D and 210D ROBIC nylon X-Grid ripstop (UHMWPE) with UTS coating, 150D polyester liner |
| Last checked | 2026-10 | 2026-09 |
Where their airline fit differs
| Airline | Limit | Kapten & Son Fyn 13L | Mountainsmith Zerk 13 UL Daypack |
|---|---|---|---|
| Air Canada | Personal item | Fits | Too big |
| Air France | Personal item | Fits | Too big |
| Allegiant Air | Personal item | Fits | Too big |
| American Airlines | Personal item | Fits | Too big |
| ANA (All Nippon Airways) | Personal item | Fits | Too big |
| British Airways | Personal item | Fits | Too big |
| easyJet | Personal item | Fits | Too big |
| JetBlue Airways | Personal item | Fits | Too big |
| KLM | Personal item | Fits | Too big |
| LATAM Airlines | Personal item | Fits | Too big |
| Lufthansa | Personal item | Fits | Too big |
| Norwegian Air Shuttle | Personal item | Fits | Too big |
| Ryanair | Personal item | Fits | Too big |
| SAS | Personal item | Fits | Too big |
| Turkish Airlines | Personal item | Fits | Too big |
| Volaris | Personal item | Fits | Too big |
| Vueling | Personal item | Fits | Too big |
| WestJet | Personal item | Fits | Too big |
| Wizz Air | Personal item | Fits | Too big |
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Specs come from each brand's own product page. Fit uses listed dimensions in any orientation. How we score carry-on fit.