I spent half the day yesterday researching base layers since i couldnt get any replies.
Here is what i did find out about so called 'best' base layers for a high aerobic activity outdoors in the winter.....
Best 'feel' next to skin. Merino Wool.
Best actual layering system for keeping warm while at same time wicking away the most sweat... skin tight Silk weight powerdry base layer with a regular wicking shirt as mid layer. Outer layer shell to either block wind or rain depending on climate. Adjust mid layer for temp.
-Wool. Merino wool has the best feel against bare skin. Keeps warm even when wet, least odor, but retains a fair amount of moisture.
-Polypro. Feels cold when mosit against skin, and has the most stink. New polypro by helly hansen and others is less odorific.
-polyester, feels cold against skin when moist.
-any of the 'chemicaly treated' fabrics dont last long. Capeline, etc is an example of chemicaly treated.
-Bi-Component fabrics work best for wicking away, while keeping a dry warm feeling next to skin.
-The best bi-component base layers typicaly come from Polartech Powerdry or Marmot Dry Clime
-base layers should be tight to skin fit to work best
-high aerobic activities (cycling) usually mean the person is generating a lot of heat so the thinnest (silk weight) variety works well.
So end result, a polartech powerdry, skin tight fit, in silk weight with a regular polyester jersey and a windbreaker or rainproof outer layer.
I couldnt find anythgin sayign what Under-Armor is made from, but i think its just a polyester in a skin tight fit. Although their cool gear wear i beleive is a bi-component so it may work well also. Its about 2x the price of powerdry though, darn marketing schemes and brand names.