Researchers developed a theoretical model for air penetration through apparel assemblies and wind induced heat transfer and applied the model to determine the effect of wind velocity, outer fabric permeability, thickness of fiber battings, and human body dimensions on the distribution of effective apparel insulation. Increasing wind velocity reduced effective thermal insulation in the windward areas. When covered with permeable outer fabrics, less permeable fiber battings showed little advantage. In strong windy conditions, effective thermal insulation increased in a manner not in proportion with the thickness of the fiber battings in the windward area and almost proportionally in the leeward area. 15 refs.