From what people said it hard cardboard, not as sturdy as hardcover books but sturdy enough, and tends to be lighter than other covers. But I'll try to talk with Incipio to see if these new ones are heavier than the first two.
If you wen to the site already you have
this thread here on MB with a review of it too
The only issue you may have with it, is that for what people say supposedly you can't fold it completely flat.
I think I can only say more when I have it on my hands.
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BTW if anyone here has it, can you tell me if the Kindle has a skin on it if it still fits inside the cover?