Originally Posted by nikhsub1
True, but then the opposite is also true. If case air is say 5C above ambient (not uncommon) then the metal res would heat the water more quickly, as the metal (copper, al whatever) is 5c hotter than ambient. In this case, the delrin would be preferred as it won't act as a heat conductor. Now if you want to install the res in a freezer, then yes metal would be much preferred. FWIW, I have a brass res that is the same size which weighs nearly 4 lbs. This one weighs maybe 8oz. I'll weigh it when I get to my office.
On a side note, I need a line of some barbs. eddy_EK has some G 1/4" barbs that are o-ring sealed as well, but dealing with him is a pain. If anyone has any ideas, give me a shout.