Snaffle bits, What ones....?

My horse goes in a snaffle bit.. I'm keeping her at my friends house and right now I am using one of their old/ extra bridles. I ordered a new one but I need to buy a bit. I herd somewhere that a bit with copper on it ( like the mouth piece) that the copper makes it more moist for the horse. Is this true... What kind would you recomend.. She uses a snaffle.