Clothes doesn't heat, is the body who produces the heat, the clothes helps you to don't loose your body heat.
The best advice to be warm in cold weather while you are doing exercice or a physical effort is not to be wet. What ever you do, never sweat, you must know how to control your body temperature, because if you sweat and your clothes get wet, soon or later will freeze and will give you a trouble. To control your body temperature while you are doing exercise is, for exemple, take out your clothes or slow down your rithm.
The way to dress in cold weather is something very personnel and the best way comes with the experience. While some people recommend a plastic bag between socks (even there are some brands who made a kind of plastic socks called "vapor barrier"), some don't. While some people use hands and feet warmers, some don't.
It is very important to know how to match your clothes, the layers... If you don't have experience we recommend you to try and test your gear in cold conditions, while you are training or enjoying a winter bivy in the mountain.
There are many videos showing how to dress in winter. Here you have this link which brings you to a Jay Petervary's video showing the gear he use when competing in the 1000 miles Iditarod Trail Invitational. For those who doesn't know, Jay is provably the best winter fatbike rider, so is good to listen his advice. In any case, and how he say in the beginning of the video: this is what's work for me.
A temperature of -15ºC could be consider very cold by many people, but between -15ºC and -20ºC the difference is very high and it's “only” five degrees less!. A few minutes without gloves at -20ºC can easy freeze your nacked hands.
When the temperature drops to -30ºC or so, everything change and you must be very careful in what you are doing. This temperature (-30ºC) is not yet considered extreme, but a little mistake can put you in big trouble. From this temperature every degree it counts.
February is not the coldest time of the year but, even then, temperatures can drop below -30ºC. So be prepared.
Please ensure that you have enough food and clothes to sustain yourself and stay safe during the all race.
In general terms, Finnish Meteorological Institute reports are generally good, thank to it is possible to have an acceptable weather reports the day before the race starts to organize your racing gear accordingly. In any case, remember that weather reports are not always right, you are in the Arctic Circle and weather can change in 15 minutes.
In case of extreme temperatures it's necessary to have a very good gear to face the cold. Also, after the tremendous effort required, and the loss of energy (calories) that this entails, even not to low temperatures can be a problem if you don't have the right good clothes.
You feel your hands cold, maybe some pain and next you have no touch on your fingertips... but is not so much, just a pain you can resist so you keep going, you use to suffer when your are competing... you feel you can hold the ski poles or the fatbike handlebar...
After a while the pain in your fingertips is over, yes is over, so you forget it... In that point your fingers are frozen. And same feeling happen with your nose and toes, etc. If you're competing in the Arctic Cicle Winter Races and you have a frostbite is your own mistake.
To avoid frostbite is as important to be well hydratated as important is to be well trained and equipated. Also is important don't have your pants, socks, shoes or whatever gear you wear so tight, your blood should flow smoothly and of course a rich diet in calories also helps to face the cold much better. If you want to know more, in internet you will find a huge amount of information about frostbite.
Frostbite in the Arctic Circle Winter Races