Damp cold feels colder than dry frost
Short answer: Damp air conducts heat away from the skin faster than dry air. That is why five degrees with rain feels colder than minus two with sun.
Moisture conducts heat away
Water conducts heat far better than air. If clothing is damp, it actively cools the body. See bamboo undershirts for men.
Windproof matters more than thick
Wind removes the warm layer of air around your body. A thin windproof layer beats a thick wool jumper. See bamboo clothing for men.
Keep the base layer dry
If the base layer is wet with sweat, the battle is lost however good the outer layer is. See bamboo t-shirts for men.
Feet first
Wet feet in damp cold are the fastest place to feel cold. Spare socks are cheap insurance. See bamboo socks for men.
Frequently asked questions
Why does damp cold feel worse?
Because water conducts heat away from the skin far faster than dry air does.
Does a thicker layer help?
Less than a windproof layer and a dry base layer. Moisture is the problem, not lack of thickness.
What should you wear next to the skin in damp weather?
A layer that moves moisture away from the skin. Never cotton directly against the body.