Roxul Industrial Insulation Process - Manual (Page 122)

2.2.9 Density
The density of mineral wool products is the amount of
fibers per cubic foot. Special care should be taken
when comparing only the densities of insulation
products. Density influences several product
performance properties. It is however not a product
performance property itself. A common assumption is
that the higher the density, the more the compression
resistance, maximum service temperature, fire
performance and thermal conductivity will improve.
This is only correct to a certain extent. A few
examples:
Binder content
During the manufacture of mineral wool products, a
binder is added to glue/form the fibers into the
desired shape. The binder content positively
influences the compression strength, but due to its
organic compounds has a negative effect on the
maximum service temperature and fire resistance.
Thermal conductivity
For high temperatures it is often better to use high
density (less radiation) mineral wool insulation.
At temperatures below 300 °F (150 °C), the conduction
throughout the fibers will be more dominant, so using
a lower density product is preferable.
Fiber structure
The (vertical, horizontal,..) orientation of the fibers
influences the longitudinal air flow resistance,
compressive strength, and thermal conductivity.
Generally, the more “vertical” fibers, the better the
compressive strength and the higher the thermal
conductivity will be.
Non-fibrous particles
Non-fibrous particles or shot content in mineral wool
products have a negative influence on the thermal
conductivity and fire resistance. For example, a
mineral wool product with a density of 6.2 lb/ft
3 (100
kg/m 3 ) and 15 % shot content, {(tested in accordance
with ASTM C 612 on a meshed netting (150 mm, 100
mesh)}, would have the same thermal conductivity as a
mineral wool product with a density of 8.7 lb/ft
3 (140
kg/m 3 ) and 40 % shot content. ProRox ® insulation are
high quality, high performing products that exceed
ASTM C612 stone wool requirements. ProRox ®
products achieve excellent thermal conductivity and
fire resistance performance, even at low densities.
Density: Nominal vs Actual
Density as per ASTM C168 is defined as “the mass per
unit volume of material”. Density is not a performance
criteria but is commonly referred to when specifying
insulation. Density is sometimes specified as Actual or
Nominal. Actual density (sometimes referred to as
Delivered density) is the true density of the insulation
and Nominal Density is the effective density of the
insulation relative to a historic benchmark where the
insulation contained 40% non-fibrous content also
known as shot (ASTM C612-99).
Insulation selection
Every mineral wool insulation product has specific
characteristics. Insulation should therefore be based
on the actual product performance, not on the density.
ASTM C612-14 states that shot should not exceed 25%
and allowable shot content has been reduced over
time in version revisions. The less shot in insulation
the greater the Nominal density. It is important to
determine if specified density is referring to nominal or
actual when reviewing insulation specifications.
A simple way to relate
Nominal density relatesto actual density in the
same way equivalent wattage of a fluorescent light
bulb relates to an incandescent light bulb. E.g. A
fluorescent light bulb with 13 watts (actual)
performs the same as 100w incandescent.
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