This work investigates the thermal insulation performances of clothing based on down and a quilting method. The effect of several parameters was studied, including the amount of down, quilting number, and their geometry. An experimental study was combined with a geometrical model to confirm that a regular hexagonal geometry is the best to maximize the heat insulation properties. For the overall tiling, the best thermal resistance was obtained by using 8.67 g of down, and the thermal conductivity is the lowest when the filling was 5.14 g down. The heat resistance was also found to increase by decreasing the quilting number, but the effect is less significant as the number increases. Also, a lower amount of down in each quilting place resulted in higher heat loss. So, improving the filling down quality helped to increase heat retention. The correct space division and filling quality lead to improved warmth retention of cold protection down products.