There are two main categories of insulation for outerwear: synthetic and natural. Synthetic insulation is exactly that: a manmade material, usually some form of polyester. Natural insulation generally only comes from one source: down, from ducks and geese. For sheer warmth, down has no competitor; but the end result is a garment that tends to be bulky or puffy, more so than is practical or desirable by the wearer, although it is the case that down has high compressibility. Another issue with down is that when it gets wet, it tends to lose loft, and performs worse. The idea behind synthetic insulators is that they perform better when wet: they don’t lose loft; they retain body heat; they keep the person warm, even if they get wet; and, they dry faster than down. There are many different brands of synthetic insulation used by outerwear companies, including Primaloft, Polarguard, and Thinsulate, and they generally perform similarly, but Primaloft is understood by many to be the best synthetic insulation.