It is made of stainless steel.
There is an adjustment on your brake light switch you might want to consider. Just follow the spring up and you will see it. Be careful though, adjusting can be counterintuitive because it is upside down.
Another thing to think about is that people pay good money for smart modules that sense when you let off the throttle and apply teh brake light switch before the brake engages. This gives cars following you a little more warning and reaction time. Something to think about.