Unlike the OnePlus One and OnePlus 2 before it, the newly introduced OnePlus X does not come with a removable back cover. So obviously OnePlus can't sell you replacement backs made out of fancy materials such as wood.
However, that hasn't stopped the Chinese company from creating a line of accessories for the OnePlus X. Only these are cases, and not back covers. The materials used are mostly the same as for the OnePlus 2's covers, though.
So you'll be able to choose from Rosewood, Sandstone, Black Apricot, Bamboo and Karbon options, along with some silicone cases coming in five colors. Three of the special ones are made from wood, while Karbon features kevlar, and Sandstone is sort of a OnePlus trademark material, having debuted as the default back cover for the 64GB OnePlus One last year.
The OnePlus X cases will be available on November 5. The silicone ones and the Sandstone case will be priced at $14.99, while the others will go for $24.99. Oh, and you won't need an invite to buy any of them.
You can't? I just ordered one today. You have to remember, Oneplus is not a big brand, they can't afford to take big losses (yet) so they make limited batches of hardware. Once they get bigger they will probably abandon the invite system altogether.
So you don't need an invite to buy the case but need an invite to buy the phone...