Traditionally, apparel has failed to provide dynamic ventilation. Particularly for those engaged in exercise or other physical activity, regulating body temperature is problematic. For example, a shirt may feel appropriate for the ambient temperature before a wearer begins a run. However, once a person has begun running, they may find the same shirt is causing them discomfort because their body temperature has increased. Traditionally, to deal with changes in temperature due to physical activity, people have had to wear multiple layers of clothing. However, once a person's body temperature has increased, the layers of clothing have to be removed to avoid discomfort and allow body heat to dissipate. Additionally, once physical activity has ceased, a person often desires to retain heat as the body begins to cool. The traditional solution to this problem has been to add additional layers. This creates several problems. First, it is very inconvenient to stop and remove layers during exercise, and the wearer is often forced to carry their removed clothing for the remainder of their activity. Second, once physical activity has ceased, the wearer begins to lose body heat. In addition to causing the wearer discomfort, this loss in body heat may lead to muscle tightness and possible injury.
Additionally, increased body temperature can be concentrated at specific areas of the body, for example, at the upper back. As a result, different areas of the body require different quantities of ventilation to maintain comfort and dissipate body heat during physical activity. Past solutions have failed to adequately address this issue.