In reply to TobyA:
> I've been a bit sceptical about the idea of winter weight base layers
The problem with thicker base layers is that they wick up, and hang on to quite a bit of moisture, isn't it?
Even though they wick away from the skin, into the bulk of the fabric, it's still there. So if it gets cold, and you press against it, you get a horrible cold, wet feeling, particularly down your back...
Thinner base layers don't have the 'reservoir' layer they can wick away and soak into, so they hold the moisture closer to the body, and it is thus encouraged to evaporate. Trouble is, that means that you tend to feel wetter all the time...
A toss-up between feeling warm and a bit damp most of the time (thin layer), or getting a bit of a cold shock every now and then with a thicker layer.
The MEC T3 is the lightest weight PowerDry I've seen, so it wicks nicely, but there isn't much 'reservoir' to hang on to much moisture.
The Techwinter things have a more solid outer 'reservoir' layer, and so can fall foul of the cold, clammy shock problem. No more so than other similar fabrics, though.