How does insulation stop heat transfer?
Heat can be transfered by two mechanisms: conductive heat and radiative heat. A thermos has a vacuum and silver lined walls, which have no conductive heat transfer (since it’s a vacuum), and minimize radiative heat transfer, since the silver walls minimize heat emission/absorption. Most household insulations are actually just means of trapping air. Air has a fairly low heat conductivity. However, if the air can circulate it will transfer heat by convection (air currents). If the air is kept still, it can only transfer by means of conduction, and this is relatively slow. The actual cellulose of fiberglass is just there to prevent air from moving!
