Yes, this widget is made of plastic.
Yes, this plastic is Polyurethane.
Yes, this Polyurethane is tough.

Some hand manipulation to show the flexibility.
Hitting the EZ Clamp Spring with some hammer blows to show it isn’t brittle.
Crushing the EZ Clamp Spring in some pliers.

Torture Testing

The 3D printed polyurethane that I use (Filaflex) in these springs has been tested to over 100,000 flexing cycles with no visible signs of wear :

Conclusions :
Testing Results :