Dear ANDI: what should I wear to be cooler in sunny and hot weather? Testing radiative performance of apparel using an outdoor thermal manikin

<jats:p>Clothing properties—including color, fit, style, and textile composition—strongly influence human radiative heat gain, the dominant heat-transfer pathway in hot, dry climates. Although textiles are increasingly engineered to reduce the heat load across the visible, near-infrared, and far-infrared regions, comparing realistic performance of such apparel is difficult because spectral measurements alone cannot capture interactions among the environment, clothing geometry, and the human body. Here, we evaluate apparel using ANDI, an outdoor, internally cooled thermal manikin exposed to direct sunlight under hot, low-wind conditions. By dynamically matching the manikin surface temperature to ambient air temperature, convective heat transfer is minimized, enabling direct measurement of net radiative heat flux. We validate the approach by comparing outdoor performance of white and black cotton and polyester shirts under natural or controlled airflow. Next, we evaluate how color, fit, style, and textile composition of upper-body garments, as well as headgear, influence radiative performance.</jats:p>