Dry down is a variety of down insulation coated with a hydrophobic treatment to help the feathers repel moisture and dry quickly. This gives dry down an advantage in wet conditions without sacrificing loft or warmth. Jackets insulated with this insulation may be slightly more expensive than some traditional down or synthetic down jackets, but they offer the latest in down insulation technology.
Synthetic down insulation uses clumps of synthetic fibers to mimic the properties of goose or duck down feathers. Although these fibers aren't as lofty as natural feathers, they do offer ample warmth. Jackets insulated with synthetic material are often more affordable and less likely to be affected negatively by moisture.
Jackets insulated with traditional down insulation are stuffed with goose and/or duck feathers. These materials are lightweight and naturally lofty, so warm air is trapped between the feathers. Although moisture has the biggest effect on this variety of down insulation, traditional down is the warmest of the three types of down.