Dry air, not warmth, determines how much clothing a body needs.

Evidence

You will laugh, but it is singular that one can face the bitter winds with the mercury at zero and below it, in exactly the same clothing which I wore in the tropics! It is only the extreme dryness of the air which renders it possible to live in such clothing. — Isabella L. Bird, A Lady’s Life in the Rocky Mountains, 228

Categorization

• QUESTION: How does humidity versus temperature actually govern perceived cold, given the author’s claim that the same tropical clothes suffice at zero degrees?