It looks like some very expensive cloth, but this dress isn't made of any material you could buy in a fabric store. And while it looks like it's light enough for a hot summer day it's also probably not something you'd actually want to put on even if you could.
This dress is the work of Alasdair Thomson, an artist who lives in Edinburgh and carves sculptures out of marble. In fact, the dresses in this collection (more photos below) are perfect recreations of clothes his friends and family donated for his project. The outfits are cut from the same type of marble as Michelangelo's "David" and Thomson created them to explore "the way fabric hangs and folds, and is attempting to capture that lightness and gracefulness in stone." Seems like he did a pretty great job!
Images via Imgur