Why are sleeping bags filled with feathers?

Sleeping bags are often filled with feathers, particularly down, because they provide Excellent insulation while remaining lightweight and compressible. Down feathers trap air, creating a warm layer that retains heat, making them ideal for cold-weather camping. Additionally, they are durable and can be packed down to a small size, making them convenient for transport. However, synthetic fills are also popular for their moisture resistance and ease of care.