It used to be the case that immersion wort chillers were almost universally made of copper. Aside from having excellent heat transfer properties, copper is a relatively soft material, and building your own DIY immersion chiller can be almost as simple as wrapping some refrigeration tubing around a coffee can or corny keg. Copper also used to be inexpensive.
But when the price of copper began its steep climb in the mid-2000s, manufacturers of wort chillers started looking to stainless as a comparatively affordable option. While copper prices may never return to pre-2005 levels, the metal is currently about 40 percent less expensive than it was 5 years ago. Nonetheless, the stainless steel immersion chiller has stuck around, and now choosing one over the other is largely a matter of personal preference.
Appearance
There will always be a part of me that prefers the look of the old-fashioned copper kettles that used to be synonymous with brewing beer. But with time, copper can develop verdigris, that greenish Statue-of-Liberty colored patina. It’s readily cleaned with a good dunk in vinegar and perhaps a bit of elbow grease, but copper does take just a bit more effort to maintain than stainless. So, if you prefer a classic look, go with copper. If you don’t want to think about it, stainless steel may be a better option.