The suction cup is made from sticky plastic. This is the most compact unit that I've ever used. I attach it to my piano.  It works great.  It should work great on a car window as well.  At this price it doesn't hurt to try it. I like it for it's simplicity, size, sturdiness, and adhesion quality.  Order multiples for big savings.  We are happy to serve you. Kindest Regards.