Good quality rubber, very tough and durable, I need one valve for a soccer ball worked great I like it because it was a pain in the butt to install and you have to be very force full with pliers and it never damaged the valve. I’m using the rest on a prototype for parts I’m making and they also were very convenient and well made no leaks ! I now need to find a fill needle with a 45-90 degree bend in it for my prototype to be easier to operate.