Cork insulation; a complete illustrated textbook on cork insulation ...

168 CORK INSULATION
capillarity, else it will become saturated with water and lose
its insulating worth entirely.
A satisfactory <strong>insulation</strong> for any purpose whatever must
be able to retard the flow of heat to an unusual degree. Many
materials will do this, but a satisfactory <strong>insulation</strong> for cold
storage temperatures must combine with such insulating
property the ability to retain its insulating efificiency for an
indefinite period under the adverse conditions of the constant
presence of moisture. Pure corkboard meets this very exact-
ing combination of these two major requirements to a degree
never yet approximated under actual operating conditions by
any other <strong>insulation</strong>.
Then, too, the delicacy of many foodstuffs makes them
peculiarly susceptible to tainting, and the <strong>insulation</strong> must
keep free from rot, mold and offensive odors, and be germand
vermin-proof; economical building construction requires
an <strong>insulation</strong> that possesses ample structural strength and in
such form that it can be installed easily in all types of build-
ings ; conservation of valuable space requires an <strong>insulation</strong>
that is compact and occupies minimum space; the reduction
of fire hazard calls for an <strong>insulation</strong> that is '^low-burning and
fire-retarding; and in the interests of economy, the insulating
material must be easily obtained and reasonable in cost. Pure
corkboard also meets these secondary but nevertheless impor-
tant requirements better than any other insulating material
that has ever been offered commercially.
81.—A Good Nonconductor of Heat.— It has been seen that
heat transference is accomplished by conduction, convection
and radiation ; and that when the problem of insulating a cold
room, for example, is under consideration, the heat transfer
by conduction is the most important, consisting of ninety per
cent or more of the total heat leakage into the room when a
suitable insulating material is employed.
It will be recalled that the heat conductivity of dense sub-
stances, such as metal, is high ;
that of lighter materials, such
as wood, is less ; while that of gases is very low. Thus air,
the most available gas, is the poorest conductor of heat, if a
vacuum is excepted, but air is a good convector of heat, unless
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