2. INSULATION MATERIALS AND PROPERTIES

2.3 PROPERTIES OF INSULATION

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Not all properties are significant for all materials or applications. Therefore, many are not included in manufacturers' published literature or in the Table of Properties which follows this section. In some applications, however, omitted properties may assume extreme importance (i.e. when insulations must be compatible with chemically corrosive atmospheres.)

If the property is significant for an application and the measure of that property cannot be found in manufacturers' literature, effort should be made to obtain the information directly from the manufacturer, testing laboratory or insulation contractors association.

The following properties are referenced only according to their significance in meeting design criteria of specific applications. More detailed definitions of the properties themselves can be found in the Glossary.

1. THERMAL PROPERTIES OF INSULATION

Thermal properties are the primary consideration in choosing insulations. Refer to the following Glossary for definitions.

a. Temperature limits: Upper and lower temperatures within which the material must retain all its properties.

b. Thermal conductance "C": The time rate of steady state heat flow through a unit area of a material or construction induced by a unit temperature difference between the body surfaces.

c. Thermal conductivity "K": The time rate of steady state heat flow through a unit area of a homogeneous material induced by a unit temperature gradient in a direction perpendicular to that unit area.

d. Emissivity "E": Significant when the surface temperature of the insulation must be regulated as with moisture condensation or personnel protection.

e. Thermal resistance "R": The overall resistance of a "material" to the flow of heat.

f. Thermal transmittance "U": The overall conductance of heat flow through an "assembly".

2. MECHANICAL AND CHEMICAL PROPERTIES OF INSULATION

Properties other than thermal must be considered when choosing materials for specific applications. Among them are:

a. Alkalinity (pH) or acidity: Significant when moisture is present. Also insulation must not contribute to corrosion of the system. See Section 3.

b. Appearance: Important in exposed areas and for coding purposes.

c. Breaking load: In some installations the insulation material must "bridge" over a discontinuity in its support. This factor is however most significant as a measure of resistance to abuse during handling.

d. Capillarity: Must be considered when material may be in contact with liquids.

e. Chemical reaction: Potential fire hazards exist in areas where flammable chemicals are present. Corrosion resistance must also be considered.

f. Chemical resistance: Significant when the atmosphere is salt or chemical laden and when pipe content leaks.

g. Coefficient of expansion and contraction: Enters into the design and spacing of expansion/contraction joints and/or use of multiple layer insulation applications.

h. Combustibility: One of the measures of a material's contribution to a fire hazard.

i. Compressive strength: Important if the insulation must support a load or withstand mechanical abuse without crushing. If, however, cushioning or filling in space is needed as in expansion/contraction joints, low compressive strength materials are specified.

j. Density: A material's density may affect other properties of that material, such as compressive strength. The weight of the insulated system must be known in order to design the proper support.

k. Dimensional stability: Significant when the material is exposed to temperature; expansion or shrinkage of the insulation may occur resulting in stress cracking , voids, sagging or slump.

l. Fire retardancy: Flame spread and smoke developed ratings are of vital importance; referred to as "surface burning characteristics".

m. Resistance to ultraviolet light: Significant if application is outdoors and high intensity indoors.

n. Resistance to fungal or bacterial growth: Is important in all insulation applications..

o. Shrinkage: Significant on applications involving cements and mastics.

p. Sound absorption coefficient: Must be considered when sound attenuation is required, as it is in radio stations, some hospital areas where decibel reduction is required.

q. Sound transmission loss value: Significant when constructing a sound barrier.

r. Toxicity: Must be considered in the selection of all insulating materials.