Shopping for a winter coat means keeping an eye out for style and warmth. Popular fabrics include wool and down; determining which will keep you warmer and most comfortable depends not just on the temperature, but also on the weather conditions your coat will encounter.

Down, made from the undercoat of ducks and geese, provides natural insulation that is both lightweight and breathable. It's also the warmest insulating material available -- natural or synthetic. Down is long-lasting and, despite being highly compressible, holds its shape well. It does not do well when wet and takes a long time to dry out. In addition to being more expensive than wool, down causes allergic reactions in some, making it a bad fit for those with sensitivities.

Wool is another effective natural insulator. Like down, it is breathable and holds its shape well. Wool may not be as warm as down, but it has a big advantage -- unlike down, wool is moisture-resistant and holds up better in wet weather. It's also more affordable than down. One downside: it's heavy. Also, like down, wool is not hypoallergenic. In fact, many find wool itchy and uncomfortable against bare skin. Wool can be blended with synthetic fibers to improve its comfort.