Blitz Powder is a material added by Thermal Foundation. It can be obtained by processing Blitz Rods, just like Blaze Powder can be obtained by processing Blaze Rods. However, it can also be created by infusing Sand with Destabilized Redstone using a Fluid Transposer.
Blitz Powder only has a single use: it is a critical ingredient for creating Aerotheum Dust, and, ultimately, Zephyrean Aerotheum.