Nickel silver rail. From a young age I've used the Peco track rubber. Apparently it's changed recently to a larger, finer block which according to friends isn't as good as the old style. Some time ago I tried Rail Zip, not sure why I stopped, maybe give it another go and report back. I clean loco wheels with the Peco rubber trimmed to a chisel point with the loco upside down and powered up.