What is the soft underlayer beneath some dogs’ topcoat called?

The story behind the answer

The soft, dense layer beneath some dogs’ topcoat is called the undercoat. It’s made of fine, downy hairs that trap air and provide insulation, while the topcoat/outercoat consists of coarser guard hairs that repel water and dirt and give the dog its visible color and texture. Although “underfur” is sometimes used informally, “undercoat” is the standard term in grooming and breed descriptions.

Many double-coated breeds—like Huskies, German Shepherds, and Labradors—