1. the soft, dense layer of fur beneath the outer guard hairs of certain mammals, providing insulation

Examples

• The arctic fox’s thick underfurs keep it warm in freezing temperatures.
• Beavers have waterproof underfurs that trap air for insulation.
• The dog’s underfurs shed heavily during spring molting season.
• Seal underfurs are so dense that water cannot penetrate to the skin.
• The trapper examined the quality of the mink’s underfurs.
• Polar bears rely on their underfurs for survival in harsh climates.