I’ve used a few different types of base layer. They are a great idea to keep comfortable, dry and warm.
On long distance rides where the weather will vary they have the promise of making whatever clothing you are wearing more able to cope with the conditions. If it is too hot then the base should help wick away sweat. If it is too cold then the base should keep you warmer.
But some types work better than others.
This is the first base layer I ever bought. It worked well, much better wicking than cotton. Unfortunately it shrank in the wash. Merkalon is apparently some sort of polyester mix.
Next I moved on to the material that all the manufacturers are pushing at the moment, merino. I had a Howies short sleeved top like the one pictured above except it was an attractive stripped red and black colour. I quickly noticed that the wicking was not as good as my old base layer, despite being made of the “latest thing”. On events it got wet with sweat but on 600s I would let it dry out on my body and the next day it was fine to use again. To me that is the main advantage of merino, it seems to able to be reused comfortably without washing
Recently when I was considering the challenge of an early season ride starting at 2am I thought that a base layer (or two) that would actually stay dry would keep me warmer than a sodden merino top. So I got the above Helly Hansen LS base and the below “string vest” mesh sleeveless base. Wearing the LS over the mesh vest proved to be both dry under the sweat load of riding and also warm.
The mesh vest in particular seems to have excellent wicking properties for someone as sweaty as me. I’ve been wearing it in cool spring conditions under a wind proof LS jersey. It seems to keep me warm(er) but I don’t end up wet with sweat
So the overall conclusion is that merino fabrics don’t work so well for me. I need something that wicks better