Ninjaflex is an exciting addition to the gamut of printable materials available to printer users. This is a really rubbery flexible material that is great for printing things like seals, gaskets, rubbery phone cases, wheels and tracks for vehicles, drive belts and much more. 
What sets ninjaflex apart from the other flexible filaments on the market is its special low tack coating on the outer surface of the spooled filament. This coating significantly eases printing by reducing the tendency for the filament to drag on the walls of the hotend or extruder. Ninjaflex has an almost powdery feeling surface before printing that seems to act like a dry lubricant of sorts, however there is no powder that sheds from the filament itself. Once the material is printed it becomes a shiny rubber like material, and regains the surface tack that you would expect, making it great for things like tyres and grippers. We would liken it to something like sillicone rubber from which phone jelly cases are made from.
Despite being one of the more easily printed materials of its type there are still some considerations to take into account when using this filament, it needs to be printed slowly in order to prevent buckling in the extruder, and your extruder needs to confine the filament from the hob all the way to the melt zone, with no free space in which the filament may buckle. Ninjaflex is not at all fussy about print surface, and will stick to most normal surfaces like glass, blue tape, and aluminium. Kapton should be avoided as it sticks very aggressively!