By Priya Anand, Backpacking Gear Research Writer · Published September 14, 2026, 6:03 PM ET
Direct Answer
Compression straps are paired webbing straps on the sides of a backpack that cinch the pack body inward when tightened. They shrink unused volume in a partially loaded pack, pull the load closer to your back for better balance, and create a loop that can hold extra gear against the outside of the pack.
In plain English
Compression straps are the pairs of flat straps running across the sides of many backpacks. When you pull them tight, they squeeze the bag smaller, a bit like cinching a belt around a loose coat.
Why would you want a smaller bag? Because a backpack that is only half full lets your gear slide around inside. Every step, that loose weight swings a little one way and then the other, and your body has to work to steady it. Pulling the straps snug keeps everything still and pressed toward your back.
They also have a handy side job. You can tuck a light, long item, like a rolled foam sleeping mat or a pair of walking poles, under the straps so it rides on the outside of the pack. Anything heavy is better packed inside, where it sits closer to you.
Compression straps solve two related problems at once: a pack that isn't full, and a load that shifts as you walk. Cinching the straps down pulls loose fabric and gear inward so the pack sits closer to your spine, which keeps the load's center of mass stable over uneven terrain instead of letting it sway independently of your body.
How many are on a typical pack?
Most hiking and backpacking packs carry two to four pairs, arranged as a top row, a middle row, and sometimes a bottom row on each side. Larger packs built for variable loads more often use three rows so different sections of the pack can be compressed independently; smaller daypacks sometimes get by with just one pair.
What else do they do?
Beyond shrinking volume, compression straps double as an improvised lashing point. Sliding a rolled sleeping pad or a pair of trekking poles under a cinched strap secures them to the outside of the pack without any dedicated hardware, though this works best for light items rather than anything heavy.
Function
How it works
Volume reduction
Cinching pulls slack fabric inward on a partly loaded pack
Load stabilization
Pulls the load's mass closer to your spine
Improvised lashing
Straps can pin a light item against the pack exterior
Both buckle types found on most packs — ladder-lock and side-release — hold tension well enough for daily cinching and releasing across a multi-day trip.
Why a stable load matters more than a small one
Shrinking the pack's outline is the visible effect, but the useful effect is what happens to the load's weight. The US Army's foot-march manual says compression straps keep the internal load from shifting and hold it closer to the body.1 That matters because a load-carriage review in Military Medicine found the lowest energy cost comes from keeping the load's center of mass as close as possible to the body's own center of mass.2
The same Army manual reports that packing heavier items higher and closer to the body can cut marching energy cost by as much as 25% compared with a low load carried away from the body.1 Compression straps do not move items up or down, but they stop a well-packed load from sagging backward and away from the spine as the day goes on.
When to cinch them in the packing process
The Appalachian Mountain Club's packing guidance puts compression at the end: pack the main compartment first, then cinch the external compression straps to shrink and stabilize the load.3 Tightening them on a half-packed bag and then stuffing more gear in simply fights the straps and can leave a lopsided load.
A useful habit is to loosen the straps before unpacking at camp and re-cinch them each morning. As food gets eaten and water is drunk, the load shrinks, and a quick pass on the compression straps takes up that new empty space so nothing starts to shift.
Designs vary, and the page's counts are a general pattern
There is no standard for how many compression straps a pack should have, and no verified source behind a specific count per pack, so treat the two-to-four-pairs figure on this page as a general observation rather than a rule. Some makers treat compression as optional. REI, for example, describes its Flash 55 as using a Packmod system of removable compression straps and pockets, so owners can strip them off to save weight or add them back for bulky loads.4
Lashing gear under compression straps is convenient but has limits. Anything strapped to the outside sits farther from your back than the same item packed inside, which works against the close-to-the-body principle above, and it can snag on brush or rock. Keep external items light, balanced side to side and tight enough that they cannot swing.
