This is how I dress for extreme cold weather. I am talking about down to -20C (-4F). Just one base layer, one mid-layer (a jersey) and a hardshell jacket.
With just this, I can cycle all of Canada. When it gets below the above temperatures, I just add an other layer between the base layer and the jersey and I am good.
At the bottom, I just wear some long johns over padded cycling shorts, long warm socks and cycling bibs.
The hardest part is keeping my fingers and my toes warm.
I have some sort of poggies that I put on the bike to protect my hands from the wind and I just wear normal gloves. When it really gets cold, I will throw in there a Zippo hand warmer to heat it up a little.
For my feet, I wear cycling boots. They are warm but not my toes get cold fast so I have had to get heated insoles too.
I have two helmets: a normal road cycling helmet for when the weather is reasonable and a ski helmet for when the temperatures are too freezing and my head needs to retain heat.
I protect my eyes with glasses and googles with clear, dark or tinted lenses depending on the conditions.
And for finally, the mode of transportation,,,
This is a Cinelli Mash SSCX bicycle set up as a fixed gear. This will be the two-wheeled vehicle that I will ride across Canada on The Big Journey. Initially, I had three bikes in mind but my Guinness World Record attempt rules stipulates that it must be done with just one.
I still have not come up with a name for this bike so any suggestions are welcome!