Chapter 1, Problem 1.33P

Wearing layers of clothing in cold weather is often recommended because dead-air spaces between the layers keep the body warm. The explanation for this is that the heat loss from the body is less. Compare the rate of heat loss for a single 2-cm-thick layer of wool $\left[k=0.04\text{W/}\left(\text{m K}\right)\right]$ with three 0.67-cm layers separated by 1.5 mm air gaps. The thermal conductivity of air is 0.024 $\text{W}\left(\text{m K}\right)$.