The Hippocase has been the best case I’ve seen to store and transport a headphone. It’s very lightweight, and yet the outer shell is very rigid, and so you can put the Hippocase inside a backpack without fear of your headphone being crushed or damaged by a sharp object inside your bag. It comes in several dimensions, the large size designed for full size headphones, as well as a medium size for Grado and other portable headphones. The Hippocase is much smaller than most boxes that comes with your headphones, and so you can throw it inside bigger bags along with your other gears. The case comes with precise cut foam to accomodate various headphone sizes, but if your headphones doesn’t fit in the foam, you can remove it and carry the headphone safely still inside the bag.
The Large Hippocase is 24cm x 24cm x 11cm, and it sells for $40.
The Small Hippocase is 19cm x 22cm x 6cm, and it sells for $25.
There is also a similar bag with the Alessandro brand.
The Alessandro Small ($25) size fits the SR60i and MS-1i headphones, where the Alessandro Medium ($40) fits the MS-Pro and RS-1 headpones.
You can get the bag directly from Jaben.net