This should come as a surprise, but they are plastic ;) also nice and light.

Comes with drainage plugs (nice!) and the rope is pretty long; perhaps a planter noob but I'm not sure why one rope length is looped and one is not - I get it, there are only three holes but I figured they'd come tied - need to look into how to do this before I hang them; ropes have metal ends to keep them from slipping through the openings on the planter