Board Thread:Speculation House/@comment-14138255-20141017020106/@comment-10390252-20141020130931

Yep; the fact that they literally evaporate is strongly indicative that they are made of some bio-mimicking substance. It is clear that this becomes unstable without an active power source. All indications is that this power source is some energy field incorporated in the body that dissipates if the Grimm is in some way seriously damaged.

At the moment it is "Your Milage May Vary" as to the source and nature of this pseudo-biotic material and energy field. It could be Clarktech (technology so advanced that it is indistinguishable from magic) or it could be something truly supernatural associated in some way with the as-yet-unknown true nature and origin of Dust.