Down is the fuzzy insulator underneath the feathers of a duck or goose. Goose down is larger and fluffier than duck, which is why they seem to be preferred. Larger down clusters provide more loft and will last longer. They are very durable, but some people do have allergies to down. Down pillows are also more expensive, but because they will last the longest with proper care they are a good bargain. You will see a fill number associated with down pillows, like 600, 700, or 800. The higher the fill number, the more loft and firmness you will have with the product.