What is the best material? We all know that replacing a cylinder head is easier and more entertaining that replacing an evaporator. Once it's done you don't want to do it or pay to have it done for another 20 years.

What is the best material?

 

FWIW, my feeling is that it is best to use a factory unit - which is copper I believe - and to pressure test it overnight before installing to ensure it is 100%. Ally matrices and similar things on XJSs have a habit of fracturing, in my experience.

That is what I did 10 years ago and no problems, yet!