Smooth plastic with smooth edges. Snapped together easily and seems sturdy. I simply have not had it long enough to say it’s durable but it is nice. I have it fastened on a play yard (at the top corner where there’s a gap in the top hem and mesh) with the pressure screw clamp but it looks like it will easily fit on a crib. It’s currently holding a simple handmade mobile on the included hanging arms (4 arms and a center hook). The music box that comes with it is mechanical and rotates for a short time. It plays “You are my sunshine” in a sweet, soft music box sound.