What is PEI+PC 3D Print material? ISS 3D Print Contest
Apparently the Made In Space printer can print an exotic alloy of PEI (ultem) and PC (polycarbonate). 


Ultem is a super-premium material for industrial FDM printers, and requires a very high temp heated build chamber to print. Hobbyists use it as a build plate -- Stratasys uses it as filament in their most expensive FDM machines. 
Polycarbonate is a specialty material that benefits from a heated chamber but is just barely printable on hobbyist level machines. (I print a fair amount of PC -- it makes ABS seem easy in comparison.) 


By alloying PC with PEI, they are presumably optimizing some kind of performance parameter compared to ultem alone or polycarbonate alone. Exactly what material properties they get will depend considerably on the ratio of the two polymers. Ultem is exceptionally heat-resistant, quite stiff, and extremely strong. PC is very heat resistant, and has exceptional impact toughness. Blends of the two can be somewhat stiffer than either, with most other properties resembling the weighted average of the two base materials. It really depends on the mix, which we don't know.

This is analogous to the PC-ABS blend filaments we sometimes use. You get reasonably intermediate properties. 

So, it's basically super-filament that NASA might want to use to make "production" parts in space. I would expect a HUGE degree of warping if not printed in extremely well-controlled conditions. But the Made In Space printer was intensely engineered for this task, so I have to assume they have it all figured out.