Mountainsmith Zerk 40 Backpack

The Mountainsmith Zerk 40 Backpack is an ultralight roll-top pack developed in collaboration with long-distance hikers, aimed at thru-hiking and multi-day trekking where every gram in the base weight matters. At 823 g for a 40 L total volume (32 L main compartment), it works out to roughly 20.6 g per liter — a ratio that puts it firmly in ultralight territory rather than standard trekking packs, which typically run two to three times heavier per liter. The body is built from 210D EXTREEMA recycled nylon ripstop reinforced with UHMPE fibers, chosen for abrasion resistance without the weight penalty of heavier fabrics. An internal frame with a contact-padded back system, removable framesheet, and detachable waistbelt lets you strip the pack down further for very light loads or leave the support in for a loaded multi-day carry. Two ice axe loops, a single front pocket, and two side pockets round out the storage, though there's no integrated rain cover or hydration port, so plan accordingly for wet-weather trips.