Insulation and Heat Balance

Insulating an object means blocking all three modes of transfer at once. The best example is the vacuum flask (thermos), a masterpiece of simple engineering:

   +----------------------------------+
   |  outer wall                      |
   |  ||  <-- VACUUM between two walls|   -> blocks conduction AND convection
   |  ||      (no matter)             |      (no medium to carry them)
   |  || silvered surfaces            |   -> blocks radiation
   |  ||   (reflect infrared)         |      (heat mirror)
   +----------------------------------+

The vacuum between the two walls eliminates conduction and convection (no matter to carry the heat), and the silvered surfaces reflect infrared radiation. Result: a drink stays hot (or cold) for hours.

The same reasoning governs the insulation of a house:

Type of loss	Remedy
losses through walls/roof	thick insulation + still air (low conduction)
losses through convection	avoid drafts, seal gaps
losses through radiation/glazing	double glazing (layer of air or gas + vacuum)

Double glazing illustrates the complete balance: two panes separated by a layer of still air or gas. Glass alone conducts little, but it is mainly the trapped layer of air (a poor conductor, and too thin for convection to set in) that insulates. Some glazing adds a thin reflective coating against radiation.

A good heat balance therefore consists in identifying, for each wall, which mode dominates the losses, and counteracting it. This is very concrete physics: it determines your heating bill and the comfort of a room.