Insulation per Unit Cost: A Clo-per-Dollar Sizing Rule for Layered Cold-Weather Garments Built from Locally Obtainable Materials

Cold harms people who cannot afford effective clothing, yet garment insulation is usually sold by brand and appearance rather than by insulation delivered per unit of money. This paper originates a clo-per-dollar sizing rule for layered cold-weather garments built from seven priced, locally obtainable fill and cloth materials: shredded cloth, dried plant fibre, cotton batting, polyester wadding, kapok, wool batting, and down. Each layer is modelled in still air by its stated conductivity, thickness, and price per unit area over a garment area of 1.5 square metres, with a fixed cloth and making allowance of 6.00 dollars. Shredded cloth delivers the most insulation per dollar, 0.860 clo per dollar per garment layer, followed by dried plant fibre at 0.782; wool batting delivers the least, 0.134, and down 0.191, despite down having by far the largest insulation per single layer, 5.161 clo. An exhaustive integer search for the least-cost stack meeting a heat-balance requirement finds that a sedentary wearer (58 watts per square metre) needs 4.59 clo at 0 degrees C, met for 11.25 dollars by two shredded-cloth layers and one plant-fibre layer; 5.98 clo at minus 10 degrees C, met for 12.75 dollars; and 7.37 clo at minus 20 degrees C, met for 14.25 dollars. Activity changes the answer more than any material choice: at minus 10 degrees C, light work lowers the requirement to 3.47 clo and the least cost to 9.75 dollars. The stacks people commonly wear fall well short when sitting still: light street clothes provide 2.08 clo, only 45.3 percent of the sedentary requirement at 0 degrees C, with a heat deficit of 56.0 watts per square metre, and a cheap two-layer polyester padded jacket provides 4.04 clo, 88.1 percent of that requirement. Warmth at rest in cold air is, on these prices, inexpensive in materials; it is the sedentary case, not the working case, that ordinary clothing fails.