Heat is
transferred through three methods: conduction,
convection, and radiation. For years, people
have focused primarily on conduction when
insulating their homes from outside
temperatures. That is why we have double-pane
windows and mass insulation. In double-pane
windows, thermal gain and loss is slowed because
the air space within the window conducts heat
more slowly than a single pane alone would
allow. The same is essentially true for
traditional fiberglass and other mass
insulators. These materials work by slowing the
speed at which heat is conducted to a cooler
surface.
Foil faced insulation is
completely different. This barrier actually
reflects radiant energy that can translate into
heat, thereby reducing gain in the summer and
loss in the winter. In fact, foil bubble
insulation can reflect upwards of 95% of the
radiant energy that strikes it. By incorporating
air bubbles, this material also reduces the
conduction of the very small percentage of
energy that it does absorb, making it even more
energy efficient.
There are
two qualities of foil faced insulation that
allow it to reduced energy transfer so
dramatically. These two qualities are high
reflectivity and low emissivity. High
reflectivity means that radiant energy is
reflected away from the surface. Radiant energy
is made up of infrared rays. Though infrared
rays are invisible to the naked eye and have no
temperature of themselves, they have the
potential to create enormous amounts of warmth
when they strike the surface of a material that
has qualities that allow absorption of the rays.
The heat created can then spread by conduction
or convection. By reflecting 95% of these rays,
foil bubble insulation inhibits heat creation.
Low emissivity means that radiant barriers
absorb and give off, or emit, very little
radiation. Because
radiant barriers absorb and
emit very little heat, they insulate all
materials behind them incredibly well.
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