Flexible 3D Printing Materials can take a number of different forms. Many polymers are flexible, for instance PET (bottles), Polyimide (Flex PCB), TPU, TPE, and blends such as Ninjaflex. Material properties can be quantified through the use of Tensile Strength or compression tests. Highly flexible materials generally having a large elongation at break and low Young’s modulus. The top flexible filaments on the market today are Ninjaflex, Semiflex, and PolyFlex.