I was skeptical of the Eagle Creek Pack-It stuff when I first saw it at REI...I already have a suitcase, so why would I want to buy more compartments to put into it? But I took a chance and I got a Pack-It Folder and the Pack-It Half Cube. This Half Cube is great for organizing my socks or underwear and can fit quite a lot given its size. Although you can roll up t-shirts and put them in here, I tend to use my Folder for pants, shorts, and shirts. I am a biologist, so when I go out of town I'm typically packing both hiking socks for work and regular socks for after work. I can easily fit 4-5 pairs of hiking socks, including some which are fairly thick, and 2-3 pairs of regular socks into this little Half Cube. I can easily fit 6 rolled up pairs of boxer shorts in a single line within the Half Cube; if you really wanted to you could probably double that by stacking them. Because the entire thing is soft, it is also fairly flexible and can accommodate more than you would expect. It zips up easily and takes up about half the space in the socks/underwear compartment in my standard carry-on size suitcase. It keeps things a little more organized than they used to be and helps me keep clean and dirty separated easier. If you want to spend extra you could get the two-sided cube and then really keep clean and dirty apart from each other, but if you don't want to spend much, this is a good deal. Check out my pictures to see the Pack-It Half Cube in action.