[Bob Sacamano]

I am building a Leibig reflux condenser for distillation. The still is going to be mainly constructed from CPVC plastic. Will the condenser perform better with a copper inner tube or equally as well with a CPVC inner tube?

[MissPhosgene]

Copper in theory, but something that won't react with any solvents will be best.... stick with the plastic.... glass if you can do it. 

[Bob Sacamano]

I am distilling ethanol so I don't believe that side rxns should be a concern (unless I am wrong). I am more concerned about the insulating characteristics of CPVC compared to copper and whether that would impact the performance of the condenser.

[MissPhosgene]

Yeah, that's why copper is better in theory. If it's just ethanol, then you probably won't have any problems. Copper shouldn't react with water or ethanol.

[Bob Sacamano]

But shouldn't the plastic eventually reach the same temperature as the water passing over it giving it the same capacity to condense as the copper?

[MissPhosgene]

Yeah. There will be an excess of water and an ethanol distillation doesn't require really high temperatures. I would use copper, but the choice is yours. Specific heat, but that also varies with temperature...

Ideally a thin walled copper tube would be best, but either way would probably be fine.

If you can, stuff some steel wool down the inner tube.

[hobobot]

I built one of these for ethanol last month. Copper actually helps purify the ethanol and make it taste better. (I'm assuming you're making vodka).  Plastic will work, and will be much easier to build with. Copper is also expensive.
I know this thread is like a week old now, but if you are still having problems let me know.