High-quality down has been a good thermal insulation material for a long time and the thermal insulation capacity of down comes from its three-dimensional structure which allows the air to stay inside the space of down cluster. At present, numerous products made of synthetic fibers in the market mimic the structure or the principle of thermal insulation of down, but the effects of their thermal insulation are still not as effective as down. Alternatively, the disadvantage of loss of thermal insulation due to moisture is often criticized by outdoor activity lovers and thus water-repellent down products currently are also available in the market. Before the water-repellent down is available, synthetic fibers are the major filling materials for most products and the best-known synthetic fiber is Primaloft which provides good thermal insulation for dry and wet situations, has good compression and recovery power, is water-repellent and has good launderability.
Most manufacturers claim their down-mimic products made of synthetic fibers are comparable to down products with FP600 to FP650 elasticity. Thus, many synthetic fiber manufacturers use down with an elasticity below FP600 for comparison and claim their down mimics products made of synthetic fibers to offer superior thermal insulation. The figure below shows the comparison results of the down-mimic fiber, Thinsulate (made by 3M). From the results, Thinsulate has good thermal gravimetric efficiency when compared with down (550 fill), but the CLO value, which indicates thermal insulation capacity, of down is still higher than Thinsulate, in spite of the fact that this may be associated with the amount of fill and thickness. For general application, CLO>2 is sufficient for use in cold-weather clothing. The material with a higher CLO value can be used in an environment with lower temperature.
Higher quality down (e.g. 600 fill to 900 fill) are expected to have better thermal insulation capacity. In summary, down products are superior to products made of synthetic fibers, regardless of the aspect of environmental friendliness or thermal insulation. The weight of synthetic cotton has to be at least twice the high-quality down to achieve the same thermal insulation capacity; therefore, high-quality down remains the first choice for developing lightweight and thermal insulating products.