**Explanation:**

Down feathers are the feathers that birds use for insulation from the cold. These feathers are specially designed to keep the bird warm by trapping air close to their body. Here is a detailed explanation of why down feathers are used for insulation:

**1. Structure of Down Feathers:**
- Down feathers are the soft, fluffy feathers found closest to a bird's body.
- They have a central shaft with numerous branching filaments that radiate outwards.
- These filaments create a loose structure that traps air.

**2. Insulating Properties:**
- The loose structure of down feathers helps to trap air close to the bird's body.
- Air is a poor conductor of heat, so trapping it in layers creates a barrier against the cold.
- The trapped air acts as an insulating layer, preventing heat loss and keeping the bird warm.

**3. Adaptation to Cold Environments:**
- Birds that live in colder climates or high altitudes have a higher number of down feathers.
- This adaptation helps them withstand the lower temperatures in their environment.
- Down feathers provide excellent insulation, allowing birds to maintain their body temperature in frigid conditions.

**4. Usage in Nest Building:**
- Birds also use down feathers in the construction of their nests.
- The soft and insulating nature of down feathers helps to provide warmth for the eggs and young chicks.
- The down feathers line the nest, creating a cozy and comfortable environment for the growing family.

**5. Harvesting Down Feathers:**
- Down feathers are commonly used in the production of high-quality bedding and clothing.
- The feathers are collected from birds during molting or after they are slaughtered for meat.
- Responsible harvesting practices ensure that the feathers are obtained without causing harm to the birds.

In conclusion, down feathers are the feathers used by birds for insulation from the cold. Their unique structure and insulating properties make them effective at trapping air and preventing heat loss. Birds that live in colder environments or high altitudes have a higher number of down feathers to help them withstand the cold temperatures. Additionally, down feathers are used by birds in nest building to provide warmth for their eggs and chicks.

Down feathers