Wool is a natural insulator, trapping air within and between its fibres. Wool insulation is enhanced by the crimp or waviness of the wool fibre. Crimp ensures the fibres stand apart from each other, ensuring still air is trapped between them. Therefore, the active response of wool to fluctuations in body temperature offers warmth when it is cold but will self-adjust when temperatures increase by releasing heat and moisture to keep a comfortable clothing climate.