It is gratifying to stand out in the sunlight on a cool or cold day and feel the warmth. Even if it is not raising your body temperature, you feel warmer. Unfortunately, the corollary is also true. Should the Sun suddenly go behind a cloud or, heaven forbid, go behind a mountain peak on the way to sunset, you may start to shiver. Again, the body may not feel it but the mind feels colder. Either of these circumstances can be readily made better by delayering in the warmth or adding a layer to retain body heat in the cold. Unfortunately, neither of these solutions is adequate to ameliorate an unanticipated event,
It is natural when going out on a cool day to take along a layer of insulation. This is properly anticipating the weather conditions. On a warm day that insulation may not be on the list of things to take on a hike. So, what are we suggesting as “extra clothing”? The word “extra” is the key. During warm conditions an extra layer of insulation is over, and above, what we expect to use on the hike. During cooler conditions where we would normally take along insulation, the “extra” is more important. It is more than what you plan to use for the day. The extra insulation is what is intended to keep you alive if you have to stay out overnight.