I would think it's a 7D fabric similar to montbell's new windshirt.
Basically a down jacket is just two windshirts sewn together and stuffed with down. That gives us only 2.2 oz per layer to make this jacket. Montbell's new Tachyon is 2.4oz (I figure losing the hood and gaining a full zipper is a wash on weight).
Since we only need one zipper for two layers, you save some weight there. Also, you get extra weight from all the extra stitching for the sewn through baffles.
Anything more than 7-Denier or similar weight fabric just won't get you the low weights that FF claims.