Down is defined as fine, soft, fluffy feathers forming the first plumage of a young bird and underlying the contour feathers in certain adult birds. The shape of a down unit or ?cluster? gives it loft and traps the air to keep you warm. Down can be one dimensional; flat with quills, two dimensional, or rounded, three dimensional or representing the shape of a dandelion seed pod. Down comes in two types, Duck and Goose. As far as the warmth factor go duck and goose are equal. The difference lies in the fact that duck down clusters take up a smaller area. In order to make a full comforter, manufacturers compensate by offering higher fill ounces for duck down. Down is actually measured in the U.S. using a method known as ?fill power?. Basically this translates into the amount of fluff the down has. The higher the fill power number the better the quality of the down fill. A fill power of 600 is considered good quality, 700-800 is considered excellent quality and anything over 800 is considered superb quality. The weight of the down blanket also makes a big difference in the warmth. When you are looking for a down comforter it is important that you know what you want in the weight and fill power. A heavy comforter will provide a lot of warmth, maybe too much if you live in a warm climate or are used to sleeping with lighter sheets. Some prefer to sleep with fewer blankets, even on a cold night so a lighter weight would be better in that case. If you prefer to bundle up and soak in the warmth, a high fill power and heavy weight would be the best choice for you. You may also want to consider purchasing a lighter weight for the summer and a heavier blanket set for the winter months. There are also regular goose or duck feathers used in bedding. These are often used in feather top mattresses and as filling for down pillows or comforters. The ratio of feathers to down will create a difference in quality and price, the more down, generally the higher the quality and price of the material. When it comes to quality bedding nothing beats the inviting warmth and softness of down comforter sets. Down clusters trap more air for its weight than any synthetic fiber. This is why a light and fluffy down comforter will keep you warmer than a blanket of the same weight filled with synthetic fibers. Ounce for ounce down provides three times the warmth than that of synthetic fibers. The millions of interlocking filaments that a down comforter has trap in the warm air and keeps out the cold. Synthetic fibers tend to clump creating cold spots. Down evenly distributes itself to cover the entire blanket. The design of the comforter also plays a role in the final quality of the set. Thread count and the correct stitching can make a big difference in the way that a comforter performs. You want to look for a down comforter that has a quilted stitch pattern with a baffle wall to keep the feathers in their own compartments to further ensure even distribution.