I used to think packing cubes were gimmicky, so I was a little stunned at what would fit in one packing cube and how useful they can be. The Tom Bihn Large Cube is made expressly for the Aeronaut carryon (see review) but, at 13.5 x 13.5 x 4.25, it will fit in almost any bag. And it holds a lot. Here’s what I got in one cube: two pairs of medium-weight pants, one long-sleeved dress shirt, one heavy wool shirt/jacket, and one t-shirt. If you pack purposefully you can fill up every square centimeter of the cube. The mesh and ripstop nylon zippered cube provides compression when fully packed, putting more clothing in less space. Plus a tightly-packed cube lends more shape and structure to a soft-sided bag than a mere pile of folded clothes can. My next project: develop a wrinkle-reducing bundle packing method for the cube.
Nice points: smooth zippers wrap around three sides for easy packing, mesh panels allow ventilation, well-made - just like the Aeronaut, reasonably priced at $18. There are a couple of other sizes and varieties available direct from tombihn.com.
BTW - here’s an account of Aeronaut packing by a convinced cube user.