Frame Types: Complete Guide

An internal-frame backpack hides its structure — usually a pair of aluminum stays, a molded plastic frame sheet, or both together — inside the pack body against a padded back panel. The frame curves to follow the spine, keeping the load close to your center of gravity. This is the frame type used on the large majority of hiking and backpacking packs sold today.

Internal frames took over the market starting in the 1970s and 1980s as hikers moved from maintained trails onto steeper, rougher terrain where a narrow, body-hugging profile mattered more than raw ventilation. Most current internal-frame packs — Osprey's Atmos AG and Aura AG, Gregory's Baltoro and Deva, Deuter's Aircontact line, Mystery Ranch's Bridger — use dual aluminum stays paired with a shaped plastic or foam frame sheet. Lighter internal-frame packs, including many from ULA and REI Co-op's Trailmade line, use a single stay or a stiff frame sheet alone to save weight while still giving the pack shape.

Internal frames hug the back for a narrow profile and better balance on uneven ground; external frames hold the pack away from the back on a rigid structure, trading some balance for airflow and easier handling of heavy or irregular loads on maintained trails. Neither type is objectively better — the right one depends on terrain and what you're carrying.

Kelty pioneered the aluminum tube external frame in the 1950s, and that basic design is still made today by Kelty and ALPS Mountaineering, among others. External frames remain popular for hauling heavy, irregular loads — a game quarter strapped to the frame, a cooler, jerry cans of water — because the rigid platform holds an odd-shaped load steady in a way a soft internal-frame pack body cannot.

Frameless packs suit hikers carrying a light total load, generally under about 20 to 25 pounds, who value low pack weight over structure and load-hauling comfort. Without aluminum stays or a plastic frame sheet, a frameless pack relies on careful packing — often a rolled sleeping pad or a removable foam pad placed against the back panel — to hold its shape and pass load down to the hipbelt.

Frameless packs suit hikers who:

• Carry a total pack weight under roughly 20 to 25 pounds on most trips
• Pack a rolled sleeping pad or foam pad against the back panel for structure
• Prioritize ounces saved over hauling comfort at higher loads
• Hike established, maintained trails rather than steep off-trail terrain
• Have practiced packing technique to keep the load's shape from sagging

Gossamer Gear's Kumo and Zpacks' Nero are examples of packs built frameless from the start. Some ultralight packs blur the line: Zpacks' Arc series uses a curved carbon-fiber frame rather than aluminum stays, and several "frameless" models ship with a removable foam pad sleeve that acts as a minimal frame when inserted.

A pack's frame routes weight down through the back panel and into the hipbelt, which should carry roughly 80% of a loaded pack's total weight off the shoulders and onto the hips. Getting that transfer right depends on both the frame and the fit — a well-built frame on a poorly fitted pack still dumps too much weight onto the shoulders.

Correct fit starts with torso length, measured from the C7 vertebra — the bony bump at the base of the neck — down to the iliac crest, the top of the hip bones. Internal-frame stays are curved to match this line, directing load down and back into the hipbelt, which should sit centered over the iliac crest, not above or below it. External-frame packs transfer load the same way in principle: the hipbelt attaches at the base of the rigid frame's lower bar, so the tubular structure carries weight down to the same hip-centered contact point.

A common guideline caps a comfortable hiking load at around 20% of body weight, though this varies with fitness, trip length and terrain. Whatever the total, a frame that fits the hiker's torso and a hipbelt that's cinched to sit on the hips — not the waist — determine how much of that load actually reaches the hips instead of the shoulders.