A computerized simulation program, INSULA, has been developed calculating the human thermal load for various climates, activities and clothing ensembles. The program includes models for thermal physiology, clothing physics and climate. The physiology model is based on one core and a shell, divided into 13 parts, from head to foot. Core temperature, skin temperature, skin blood flow, sweat rate, wet skin surface, heat storage, and heart rate are calculated. The metabolic rate (heat production) is obtained from a list of activities or by selecting foot and ski (w/wo sleigh) march speed, terrain factor, slope and the mass of the carried burden. From the clothing model insulation and water vapour resistance are estimated for multi-layer ensembles. The thermal IR signature can also be displayed. A Wardrobe holding about 200 items is available. An item is characterized by its material thickness and body parts covered. The material of each part of the garment can be either permeable, impermeable or semipermeable (two resistance levels) in respect of liquid/vapour transport. The fitting that i.e. governs clothing ventilation can either be "tight", "loose" or "very loose". External ventilation can be supplied. Effects of wind and walking speed are included. Climate is based on data for numerous places world wide. The longitude and latitude of a site decide the hourly variations in temperature, humidity, solar radiation (standing human). Air speed, cloudiness and reflectivity of the ground are selected in menues. The simulation program is partly validated but more validation work is needed. INSULA can be reached from internet by e-mailing a special spreadsheet to the INSULA-computer.