copper, done it cools itself, does not rap moisture, just pitch the pipes about 1/8th inch per 10 ft to a corner and put a drain, another tip is to use t's and come out of the top of the copper, and down and around so water in the pipe does not run down the outlet, i will get a pic of my shop, i ran 1.50 main line with 3/4 drops, and had my air take offs t off to the side also.
no moisture period.
