"It's not the heat but the humidity" is an often expressed opinion about the thermal environment that is familiar to us all. But in spite of the universality of this feeling, the truth of the matter is that we actually know very little about relative humidity. The layman, while having a general idea about its meaning, is hard pressed to define it. The medical profession harbors conflicting views on its health aspects, and only scattered reports are available on its effect upon performance. Yet, despite these facts, we are witnessing an increased emphasis on the role of humidification and dehumidification on our work and living environments.

This paper reviews and discusses earlier research on comfort and humidity and relates the findings to the energy crisis and government regulations in place in the mid-1970s.