In many cases, building envelope design is mostly a matter of aesthetics and costs. As attention to environmental issues grows, however, sustainability and energy-related concerns play an increasing role in these decisions. The push to reduce urban heat island effects is one of the most prominent of these concerns.

Although both wet-bulb globe temperature and Heat Index take into consideration dry-bulb temperature and relative humidity, Heat Index is calculated specifically for outdoor shaded areas and does not consider conductive heat transfer from wind speed or the heat stress added by direct sun exposure.