This is a eSUN eLastic (TPE-83A)-Black-1kg/spool. The plastic is a TPE, or Thermoplastic Elastomer, which is a combination of copolymers or polymers like plastic and rubber. This gives it amazing bending and flexural strength, with an impressive elongation before breaking as well, allowing it to be used for very unique applications – especially since you can print your own custom 3D Printing designs
