Mountainsmith Zerk 40 UL Backpack vs Rab Syclon XP 40L Waterproof Pack
The Mountainsmith Zerk 40 UL Backpack is 40L and 0.97kg2.1lb; the Rab Syclon XP 40L Waterproof Pack is 40L and 0.89kg2lb. The Rab Syclon XP 40L Waterproof Pack is 0.08kg0.2lb lighter. The Rab Syclon XP 40L Waterproof Pack costs $4.949999999999989 less. The Mountainsmith Zerk 40 UL Backpack fits the carry-on limit of 30 of 36 major airlines and the Rab Syclon XP 40L Waterproof Pack fits 0; under the seat, 0 and 0 of 26.
| Spec | Mountainsmith Zerk 40 UL Backpack | Rab Syclon XP 40L Waterproof Pack |
|---|---|---|
| Price | $229.95 | $225Best |
| Volume | 40L | 40L |
| Expands to | 44L | n/a |
| Weight | 0.97kg2.1lb | 0.89kg2lbBest |
| Carry-on compliance | 83%Best | 0% |
| Personal-item compliance | 0% | 0% |
| Dimensions | 50.8×30.5×22.9cm20×12×9in | 63×34×28cm25×13.5×11in |
| Laptop | no laptop sleeve | n/a |
| Bottle pockets | 2 | n/a |
| Opening | Roll-top, Roll top closure with V-strap compression | Roll-top, Roll top entry |
| Warranty | Lifetime | Lifetime |
| Torso length | 40.6 to 53.3cm (16 to 21in) | n/a |
| Organizer | No | No |
| Shoe compartment | No | No |
| Hydration sleeve | Yes | Yes |
| Frame sheet | Removable | No |
| Water-resistant | No | Yes |
| Rain cover | No | No |
| MOLLE | No | No |
| Hip belt | Removable | Yes |
| Sternum strap | Yes | Yes |
| Load lifters | No | No |
| Shoulder strap | No | No |
| Luggage pass-through | No | No |
| Camera compartment | No | No |
| Material | 210D and 100D Robic nylon X-Grid Extreema (UHMWPE) ripstop with UTS coating, Spundura stretch mesh, 150D polyester liner | 40D high tenacity nylon (100% recycled), 100D (85% recycled) high tenacity nylon with Spectra Ripstop |
| Last checked | 2026-09 | 2026-10 |
Where their airline fit differs
| Airline | Limit | Mountainsmith Zerk 40 UL Backpack | Rab Syclon XP 40L Waterproof Pack |
|---|---|---|---|
| Air Canada | Carry-on | Fits | Too big |
| Air France | Carry-on | Fits | Too big |
| AirAsia | Carry-on | Fits | Too big |
| Alaska Airlines | Carry-on | Fits | Too big |
| Allegiant Air | Carry-on | Fits | Too big |
| American Airlines | Carry-on | Fits | Too big |
| ANA (All Nippon Airways) | Carry-on | Fits | Too big |
| Avianca | Carry-on | Fits | Too big |
| British Airways | Carry-on | Fits | Too big |
| Cebu Pacific | Carry-on | Fits | Too big |
| Delta Air Lines | Carry-on | Fits | Too big |
| easyJet | Carry-on | Fits | Too big |
| Frontier Airlines | Carry-on | Fits | Too big |
| Gol Linhas Aereas | Carry-on | Fits | Too big |
| IndiGo | Carry-on | Fits | Too big |
| JetBlue Airways | Carry-on | Fits | Too big |
| KLM | Carry-on | Fits | Too big |
| LATAM Airlines | Carry-on | Fits | Too big |
| Lufthansa | Carry-on | Fits | Too big |
| Norwegian Air Shuttle | Carry-on | Fits | Too big |
| Qantas | Carry-on | Fits | Too big |
| SAS | Carry-on | Fits | Too big |
| Singapore Airlines | Carry-on | Fits | Too big |
| Southwest Airlines | Carry-on | Fits | Too big |
| Turkish Airlines | Carry-on | Fits | Too big |
| United Airlines | Carry-on | Fits | Too big |
| Vietjet Air | Carry-on | Fits | Too big |
| Volaris | Carry-on | Fits | Too big |
| WestJet | Carry-on | Fits | Too big |
| Wizz Air | Carry-on | 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.