Because the cotton contains more air among its fibres, and air is a poor conductor of heat.
Why is a woollen shirt warmer than one made of cotton?
Because wool contains more air among its fibres, and is, therefore, a poorer conductor of heat.
Why is fur warmer than wool?
Because there is more air among the hairs of the fur, and it is, therefore, a poorer conductor of heat.
What fur is the warmest?
Fur with very fine hairs, like that of the rabbit, because it contains the most air.
Why is fur warmer when the hair is next to our bodies?
Because the fur and the air in it both help to keep the heat of our bodies from passing off rapidly.
Is the earth a good conductor of heat?