For a couple of nights when moving from hut to hut or truly covering some ground, the Patagonia 36 Litre Altvia Backpack features a highly breathable back panel and shoulder straps, plus a frame that supports heavier loads, for going the distance in comfort. Made of rugged 100% recycled nylon. Features and Specifications Built of rugged 100% recycled nylon Highly breathable Regulator® airmesh shoulder straps and hip belt Suspended mesh back-panel construction provides excellent airflow and prevents moisture buildup for all-day comfort On-the-go accessible hip belt and side pockets secure small items while on the move Sleeve can hold gear and is also hydration compatible Rain cover included Lid and internal security pockets zip to keep items safe 992 grams Materials: Shell: 4-oz 140-denier 100% recycled nylon ripstop. Boot: 4.1-oz 210-denier 100% recycled nylon ripstop. Rain cover: 2.2-oz 100% recycled polyester taffeta. All with a PU coating and a PFC-free DWR finish (durable water repellent coating that does not contain perfluorinated chemicals). Back panel and straps: 100% polyester mesh. Stretch-mesh pockets: 9.4-oz 66% nylon/34% spandex. Lining: 3-oz 200-denier 100% recycled polyester with a PU coating Measuring Your Torso To Determine Your Pack Size Take a couple of minutes to accurately measure sizing will yield the best fitting pack possible. Follow these 3 easy steps:1. Find the Iliac crest (the top of the hip bone)2. Find the C7 Vertebra (the largest bump at the base of your neck)3. Measure from the C7 down along the spine to where it intersects with the Iliac Crest. Use the table below to then determine your correct pack size. Patagonia Technical Backpack Sizing Table  Size Range Suit Torso Length Suit Waist Small / Medium 16"- 19" 28"- 36" Large / Extra Large 19"- 22" 32"- 42" Patagonia Altvia 36 Litre Lightweight Hiking Day Pack with Raincover