A hydration pack is a backpack that carries water in an internal reservoir (bladder) connected to a drink tube, allowing the wearer to sip hands-free without stopping or removing the pack. Available from minimal running packs to larger hiking and biking versions, it makes frequent drinking effortless — encouraging better hydration — though the bladder can be harder to refill and monitor than bottles.
Lumens are the unit measuring the total amount of visible light a source emits — its overall brightness. For headlamps and flashlights, a higher lumen rating means a brighter maximum output, but lumens alone don't tell the whole story: beam distance, beam pattern, and runtime matter just as much for real-world use on the trail.
A satellite messenger is a handheld device that uses commercial satellite networks to send and receive text messages, share location tracking, and trigger an SOS to emergency services from areas with no cell coverage. Unlike a one-way PLB, satellite messengers offer two-way communication and check-ins, but require a paid subscription. They're a popular safety and communication tool for remote backcountry travel.
A PLB (personal locator beacon) is a compact emergency device that, when activated, transmits a distress signal with your GPS location via the government-operated Cospas-Sarsat satellite network to search-and-rescue authorities. Designed for life-threatening emergencies, PLBs require no subscription, broadcast on the powerful 406 MHz frequency, and are a reliable last-resort safety tool for the backcountry.
A GPS watch is a wrist-worn device that uses satellite positioning to track your location, distance, pace, speed, and route, often alongside metrics like elevation, heart rate, and navigation. Popular with hikers, trail runners, and mountaineers, it combines fitness tracking with backcountry navigation features, and ranges from simple running watches to rugged multisport units with full mapping.
A 3-in-1 jacket (or interchange jacket) is a two-piece system combining a waterproof outer shell with a zip-in or snap-in insulating inner layer (often fleece or a puffy) that can be worn three ways: shell alone for wet weather, inner alone for cool dry conditions, or both together for cold and wet. It offers versatility and value in one purchase, at some cost in weight and optimized performance.
A windbreaker, or wind shell, is an ultralight, highly packable jacket designed to block wind and shrug off light moisture while remaining far more breathable than a rain jacket. It adds significant warmth for its tiny weight by stopping wind chill, making it a favorite active layer for hiking, running, and fast-moving days in cool, dry-to-damp conditions.
An insulated jacket is a layer that adds warmth by trapping body heat in lofted insulation — either natural down or synthetic fill. It's worn as a mid-layer or outer warmth layer in cold conditions. Insulated jackets are broadly divided into warm, packable 'static' puffies for when you stop moving, and breathable 'active' insulation designed to be worn during exertion.
Pack volume is the carrying capacity of a backpack, measured in liters — the total amount of gear it can hold. It's the primary way packs are sized, from small daypacks (~15–30L) to multi-day backpacking packs (50–70L) and expedition packs (70L+). Choosing the right pack volume means matching capacity to your trip length, gear bulk, and how lightweight your kit is, so the pack is big enough without being oversized.
Load lifters are the straps that run from the top of a backpack's shoulder straps up to the top of the pack frame, used to pull the upper part of the load in toward your body. Properly adjusted, they prevent the pack from pulling backward, improve balance and stability, and shift weight efficiently between the shoulders and hips. They're a key part of dialing in a comfortable, well-fitted backpack carry.
