4. Cold and water
In winter, when it is freezing cold and can be also
pretty wet, you can get enough protection only with
neoprene material. It is well known from water sports.
When it gets wet, it traps a layer of water, which is
then heated by your body and thus the warm protection is
Shoe gaiters and gloves are the most common examples
of neoprene use in biking. If you use XC SPD shoes, then
you absolutely must use the gaiters, since SPD cleats
connected to the soles of the shoes result in very cold
feet. If you want more regular winter riding, then you
should buy special winter cycling shoes. But these are
rare on the market.
Then you can also have neoprene face mask and a
baklava, which are both needed in extreme cold.
Of course it is wise to protect your head in the cold
as well. The simplest is a thin Wind Stopper hat, that
you put under your helmet.