Insulator

Conductors are materials that allow heat or electrical energy to easily move through them.

Insulators are materials that do not easily allow heat and electrical energy to move through them.

The hair on animals and people trap tiny pockets of air and that air acts as insulator. Air is a good insulator. It will keep the heat inside the body of a person or animal.

A thermos is designed to prevent conduction, convection and radiation. The glass/plastic that holds the hot liquid is an insulator so heat cannot transfer easily through conduction.

The thermos is also designed to prevent heat loss through convection. The thermos has a vacuum where there is not air. Heat cannot easily transfer through convection.

The thermos is designed to prevent heat loss through radiation. The silver coating inside the glass/plastic that hold that hot liquid reflects the heat back into the liquid.