Down Filled garments are generally available in the form of Down Jackets and Down Gilets. A Down product is a piece that has been Down Filled to create a highly insulated garment. The two most common types of down available are goose down and duck down. These are essentially natural goose and duck feathers. Created by mother nature, goose and duck feathers have exceptional insulating qualities, and outperform synthetic man made fibres for heat retention.
Garments filled with down are usually not waterproof, but only water-resistant. This is because during the manufacturing process, this type of garment has to be stitched through to hold the down in place. As such, down gilets and down jackets are more commonly used in dry environments, or used as a Mid Layer underneath an outer shell in high altitude mountaineering. Down Filled garments are also often used by climbers stood stationary, belaying their ascending climbing partner. A down jacket used for this purpose is known as a belay jacket, where the aim is to keep the stationary belayer warm.
Another advantage of Down Filled products is that they generally pack down well and can be stashed. This is an extremely useful advantage, as you would often be too warm wearing an outdoor clothing down garment when participating in high activity outdoor pursuits and as such would have to take the garment off and stash it in your Rucksack.