All references to temperature are wind chills.
The tight: the previous iteration of the Sugoi Firewall. I wore these 95% of the time and I can prove it. Windproofing is the key for me in all this winter gear. The fabric is tough too. It survived a January 30 pavement slide without so much as a scuff. I used the tight alone starting at 50 degrees down to about 15 degrees.
The long underwear: to squeeze a little more use out of the tights I put a pair of long underwear underneath. The underwear is a very light, thin, and cheap polypropylene fabric. Thin is important because thickness restricts motion making for more difficult miles. The undies paired with the tights got me down to about 5 degrees.
The extremes: below 5 degrees I tended toward a Smart Wool Midweight Tight coupled with the (legendary if you believe the marketing (I did!)) Mile Marker Sports XC Cross Pant. The Smart Wool Midweight Tight is you guessed it, 100% wool. 1 billion sheep can’t be wrong, eh? The Mile Marker Sports XC Cross Pant is made from their secret blend of 85% polypropylene and 15% lycra. Oops, I’ve said too much. Just call it 3SP.
I rode twice at –(7) windchill. Once with the long underwear/tight option and once with the wool tight/XC Pant option. Both times my leg perceived comfort was 0 (perfect). It’s likely that the XC Pant and the wool tights are just another option and not necessarily a necessity for extreme cold.
But options are important because once in a while the stuff has to go through a laundry cycle. To be a little easier on The Wife (who has not certified me to do laundry) I don’t wash my leggings after every ride. Last winter I stayed alert and evaluated each piece daily usually washing pieces the day after they needed it.