Why is cashmere so warm and light weight?

Cashmere by definition is an opaque corrugated fiber with a diameter between 14/18 micron (much finer than Merino wool, the finest wool from sheep, which is about 24 microns in diameter). Cashmere has an insulating power 10 times greater than that of wool. Therefore it is warmer and lighter due to its special structure made of air chambers that favor thermal insulation from both heat and cold.