“As an insulator, we’d like to say that evolution has occurred in nature’s R&D department – not in some lab creating a synthetic fiber that is from the onset just not going to perform as well,” said Legge.

Source: https://www.kunc.org/regional-news/2023-02-26/from-wool-to-hemp-sustainable-building-materials-are-a-growing-business-in-the-mountain-west

Trapped air between the layers acts as an insulator.

Source: https://wibx950.com/ixp/39/p/snow-to-kick-off-work-week-in-cny-dangerously-cold-temps-to-end-it/