Summary

The general idea of a layering system on your upper body is that:
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1.    A base layer will wick sweat away from your body
2.   A mid fleece layer will provide insulation, and
3.   An outer shell layer will provide protection from the wind.

Only two layers are necessary on the legs (base layer and outer shell) or you will otherwise overheat.

Please Note: It is recommended that you bring two or three sets of base layers for your legs and torso, and an extra fleece for your torso. You will only wear one base layer on your legs and upper body while running, but you can change into the additional dry base layers during the race if you are getting cold and wet. Keeping dry is important in cold conditions! Extra pairs of gloves and socks are recommended for similar reasons.
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‍Many adventure / outdoor shops should be very familiar with a layering system and will be able to advise you on what to wear when running in very cold weather.

We listed some sample links on this page for your reference - they are examples from a variety of sources and brands of what will work. You can also check out websites below for further examples / options of appropriate clothing.
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‍www.marmot.com
‍www.patagonia.com
‍www.mountainhardwear.com
‍www.columbia.com
‍www.rei.com
www.arcteryx.com