Swan and goose down is the dearest and most famous kind of bird feathers, known as an excellent insulator. It keeps swans warm to temperatures as low as -10 degrees Celsius.
天鵝的羽毛是世界上名貴的絨毛，極具保暖性，能保護著天鵝生存在攝氏零到十度的低冷環境中。