Close the main zip first, with the cube packed to around 80-90% of its uncompressed capacity rather than completely full — this leaves the slack the second zip needs to actually pull the sides together and force air out.
Compressing an overstuffed cube mostly just strains the zip track rather than reducing volume, and is one of the more common reasons a compression cube gets returned as “not working” when the packing method, not the cube, was the issue.
What travelers ask
Why isn't my compression cube actually getting smaller?
The most common cause is overfilling the cube before closing the main zip, leaving no slack for the compression zip to remove. Pack to roughly 80-90% of the cube's uncompressed capacity, then compress — trying to force a fully stuffed cube shut strains the zip without reducing volume.
Last reviewed 26 August 2026