there is no real difference between TPU (thermoplastic polyurethane) and Ninjaflex. Ninjaflex is just the most common brand for elastic filament and prooves to produce very high quality material. Ninjaflex is (on the chemical point of view) the absolutely same material, however the purity of the material aswell as the consistend diameter of the filament make Ninjaflex one of the best choises for flexible parts.
Cheaper brands may have impurities in the filament that can cause a rough surface aswell as an overall weaker print, more on that later.
You can have a look at technical properties aswell as the safety data sheet when clicking this link:
The filament prooved to have very much surface friction aswell as “adjustable” flexibility depending on the infill.
If you go for low infill density like 20% the filament the parts will be very bendable, however they are not as durable as solid parts. The elongation before breaking is about 400% so you can expect very much flexiblity from this material.
However due to the method of printing layers, that most printers (aswell as mine) use you should expect the part to break at 250-300% elongation depending on the direction you are pulling and the infill. The parts tend to be weaker when trying to pull layers apart compared to attempting to break along the printing direction.
However i have not yet archieved it, to break a 1mm thick disc (size of normal CD) just by pulling on it with bare hands, no matter what direction and angle i pull from. Just with pliers and a little bit of cutting i was able to break it in two halfs.
I hope this helps you to decide if Ninjaflex is the right material for your application.
At the moment i have no pending order and could start printing immediately.