None. You are likely to enjoy reading with the Forma most if you use it as designed, uncased, because it is light, grippy, and comfortable to hold. One of the very things I love about the Forma is you don't NEED a case to make it super comfortable to hold, and this is a big competitive advantage vs the Kindle Oasis. Which was slippery and uncomfortable for me, no idea what Amazon was thinking there. For transport, as others said, just get a cheap zip cover about the right size to give your Forma some padding and throw it in a backpack.