Compression sack

A compression sack is a fabric stuff sack with external straps, or sometimes a roll-and-seal valve, used to squeeze the air out of soft items such as clothing, a sleeping bag, or a packable jacket, shrinking their packed size significantly compared to just folding them into a bag. They are similar in purpose to compression packing cubes but usually round or cylindrical rather than rectangular, and often built from slightly heavier fabric.

For one-bag travel, compression sacks are most useful for bulky items that do not need to stay wrinkle-free, such as a down jacket, a fleece, or extra layers for a cold climate trip, since heavy compression can crease dressier clothing. They reduce volume more than weight, so a compression sack helps fit more into a fixed size bag but does not make the load lighter to carry.

When choosing one, match the sack's size to the specific bulky item you are compressing rather than buying the largest available, and check the fabric's durability if you plan to compress and release it repeatedly on a trip. A common mistake is compressing delicate or structured clothing, such as a blazer, which can come out permanently creased in a way that is difficult to fix without an iron.