Why does surrounding air absorbs heat from body while it is insulator?

Air will only absorb heat from a body if it is at a lower temperature. Being an insulator does not mean that something will not absorb heat, it just means that heat moves through it slowly. Since air has such a low density, the molecules in it are widely spaced compared to a liquid or solid and conduction of heat through the air is very slow since the molecules do not collide nearly as frequently as they do in more dense materials.