Trying to Understand Evolution of Patagonia Base Layers

So would I.  I actually called their customer support to determine what Polartec style # is used for the Thermal weight.  I think I know the answer, but cannot be sure.  They promised to get back to me, but never did.  My guess is that the present thermal weight is actually less warm than the mid weight version.  Probably not significant in use.  I would also wager that the midweight wicks more effectively than the thermal, based on the construction.  I have an old thermal weight base layer.  It does not wick at all.  The hydrophilic chemical treatment is likely washed out. Over the years, they have made fabric changes without corresponding name changes.  So, it is anybody’s guess.  I guess at the very least, I need to purchase one of each and measure both warmth and wicking performance.  For older versions, if anyone wants to donate, I can test them as well.  They way the testing will go, the shirts may be cut up to facilitate testing, so anyone sending a shirt may not get them back.  PM me if you have an old Capilene shirt to contribute.  The shirt should be in good condition.  It should be size large or bigger.