I am the UK beta tester for Filaflex, I also have NinjaFlex.

They are both Thermoplastic Polyurethanes (TPU).

The difference is the temperature they are extruded at during the manufacturing phase.

I can snap 1.75mm Ninjaflex by stretching it with my hands, Filaflex I can not.

Filaflex is more elastic.

Ninjaflex can be slightly easier to print due the surface roughness of the filament (due to extrusion temperature during manufacture)

Filaflex prints on cold glass.

Ninjaflex is recommended to be printed on a heated bed, although some users print on cold glass too.

Filaflex Safety Data Sheet : http://recreus.com/en/index.php?cont...d_attachment=8
Ninjaflex Safety Data Sheet : http://www.fennerdrives.com/FetchFil...a-e81b22ce9ad0

See my blog for more tips on flexible printing : http://www.gyrobot.co.uk/blog/how-to...ible-filaments
http://www.thingiverse.com/Gyrobot/designs