Click here to visit
the MTL Product Catalog
Manufacturers Technical Literature
This site presented by
NIA | National Insulation Association

Insulation Materials

Definition of Insulation
Generic Types And Forms Of Insulation
Properties Of Insulation
Major Insulation Materials

Insulation is defined as those materials or combinations of materials which retard the flow of heat energy by performing one or more of the following functions:

1. Conserve energy by reducing heat loss or gain.
2. Control surface temperatures for personnel protection and comfort.
3. Facilitate temperature control of a process.
4. Prevent vapor flow and water condensation on cold surfaces.
5. Increase operating efficiency of heating/ventilating/cooling, plumbing, steam, process and power systems found in commercial and industrial installations.
6. Prevent or reduce damage to equipment from exposure to fire or corrosive atmospheres.
7. Assist mechanical systems in meeting USDA (FDA) criteria in food and cosmetic plants.

The temperature range within which the term "thermal insulation" will apply, is from -73.3ºC (-100ºF) to 815.6ºC (1500ºF). All applications below -73.3ºC (-100ºF) are termed "cryogenic," and those above 815.6ºC (1500ºF) are termed "refractory."

Thermal insulation is further divided into three general application temperature ranges as follows:

A. Low Temperature Thermal Insulation

1. 15.6ºC through 0ºC (60ºF through 32ºF) -- i.e. Cold or chilled water.
2. -0.6ºC through -39.4ºC (31ºF through -39ºF) -- i.e. Refrigeration or glycol.
3. -40.0ºC through -73.3ºC (-40ºF through -100ºF) -- i. e. Refrigeration or brine.
4. -73.9ºC through -267.8ºC (-101ºF through -450ºF) -- i. e. cryogenic.

B. Intermediate Temperature Thermal Insulation

1. 16.1ºC through 99.4ºC (61ºF through 211ºF) -- i.e. Hot water and steam condensate.
2. 100.0ºC through 315.6ºC (212ºF through 600ºF) -- i.e. Steam, high temperature hot water.

C. High Temperature Thermal Insulation

1. 316.1ºC through 815.6ºC (601ºF through 1500ºF) -- i.e. Turbines, breechings, stacks, exhausts, incinerators, boilers.

Insulation will be discussed in this manual according to its generic types and forms. The type indicates composition (i.e. glass, plastic) and internal structure (i.e. cellular, fibrous). The form implies overall shape or application (i.e. board, blanket, pipe insulation).


1. Fibrous Insulation: Composed of small diameter fibers which finely divide the air space. The fibers may be perpendicular or horizontal to the surface being insulated, and they may or may not be bonded together. Silica, rock wool, slag wool and alumina silica fibers are used. The most widely used insulation of this type are glass fiber and mineral wool.

2. Cellular Insulation: Composed of small individual cells separated from each other. The cellular material may be glass or foamed plastic such as polystyrene (closed cell), polyurethane, polyisocyanurate, plyolefin, and elastomeric.

3. Granular Insulation: Composed of small nodules which contain voids or hollow spaces. It is not considered a true cellular material since gas can be transferred between the individual spaces. This type may be produced as a loose or pourable material, or combined with a binder and fibers to make a rigid insulation. Examples of these insulations are calcium silicate, expanded vermiculite, perlite, cellulose, diatomaceous earth and expanded polystyrene.


Insulation is produced in a variety of forms suitable for specific functions and applications. The combined form and type of insulation determine its proper method of installation. The forms most widely used are:

1. Rigid boards, blocks, sheets, and pre-formed shapes such as pipe insulation, curved segment, lagging, etc.: Cellular, granular, and fibrous insulations are produced in these forms.

2. Flexible sheets and pre-formed shapes: Cellular and fibrous insulations are produced in these forms.

3. Flexible blankets: Fibrous insulations are produced in flexible blankets.

4. Cements (insulating and finishing): Produced from fibrous and granular insulations and cement, they may be of the hydraulic setting or air drying type.

5. Foam: Poured or froth foam used to fill irregular areas and voids. Spray used for flat surfaces.


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 in 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 (Section XI).

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

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

b. Thermal conductance "C": The rate of heat flow for the actual thickness of a material.

c. Thermal conductivity "K": The rate of heat flow based on 25 mm (one inch) thickness.

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 "system" to the flow of heat.

f. Thermal transmittance "U": The overall conductance of heat flow through a "system".

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

a. Alkalinity (pH or acidity): Significant when corrosive atmospheres are present. Also insulation must not contribute to corrosion of the system. See Section III.

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.

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

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

f. Chemical resistance: Significant when the atmosphere is salt or chemical laden.

g. Coefficient of expansion and contraction: Enters into the design and spacing of expansion/contraction joints and/or the 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 affects other properties of that material, especially thermal properties.

k. Dimensional stability: Significant when the material is exposed to atmospheric and mechanical abuse such as twisting or vibration from thermally expanding pipe.

l. Fire retardancy: Flame spread and smoke developed ratings should be considered.

m. Hygroscopicity: Tendency of a material to absorb water vapor from the air.

n. Resistance to ultraviolet light: Significant if application is outdoors.

o. Resistance to fungal or bacterial growth: Is necessary in food or cosmetic process areas.

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

q. Sound absorption coefficient: Must be considered when sound attenuation is required, as it is in radio stations, some hospital areas, etc.

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

s. Toxicity: Must be considered in food processing plants and potential fire hazard areas.


The following is a general inventory of the characteristics and properties of major insulation materials used in commercial and industrial installations. See the Insulation Property Tables at the end of Section II for a comparative review.


Calcium silicate is a granular insulation made of lime and silica, reinforced with organic and inorganic fibers and molded into rigid forms. Service temperature range covered is 37.8ºC to 648.9ºC (100ºF to 1200ºF). Flexural strength is good. Calcium silicate is water absorbent. However, it can be dried out without deterioration. The material is noncombustible and used primarily on hot piping and surfaces. Jacketing is field applied.


a. Fibrous: Available as flexible blanket, rigid board, pipe insulation and other pre-molded shapes. Service temperature range is -40.0ºC to 37.8ºC (-40ºF to 100ºF). Fibrous glass is neutral; however, the binder may have a pH factor. The product is noncombustible and has good sound absorption qualities.

b. Cellular: Available in board and blºCk form capable of being fabricated into pipe insulation and various shapes. Service temperature range is -267.8ºC to 482.2ºC (-450ºF to 900ºF). Good structural strength, poor impact resistance. Material is noncombustible, non-absorptive and resistant to many chemicals.


Rock and/or slag fibers are bonded together with a heat resistant binder to produce mineral fiber or wool available in loose blanket, board, pipe insulation, and molded shapes. Upper temperature limit can reach 1037.8ºC (1900ºF). The material has a practically neutral pH, is noncombustible, and has good sound control qualities.


Perlite is made from an inert siliceous volcanic rock combined with water. The rock is expanded by heating, causing the water to vaporize and the rock volume to expand. This creates a cellular structure of minute air cells surrounded by vitrified product. Added binders resist moisture penetration and inorganic fibers reinforce the structure. The material has low shrinkage and high resistance to substrate corrosion. Perlite is noncombustible and operates in the intermediate and high temperature ranges. The product is available in rigid pre-formed shapes and blocks.


Foamed resins combined with elastomers produce a flexible cellular material. Available in pre-formed shapes and sheets, elastomeric insulations possess good cutting characteristics and low water and vapor permeability. The upper temperature limit is 104.4ºC (220ºF). Elastomeric insulation is cost efficient for low temperature applications with no jacketing necessary. Resiliency is high. Consideration should be made for fire retardancy of the material.


Insulation produced from foaming plastic resins create predominately closed-cellular rigid materials. "K" values decline after initial use as the gas trapped within the cellular structure is eventually replaced by air. Check manufacturers' data. Foamed plastics are light weight with excellent moisture resistance and cutting characteristics. The chemical content varies with each manufacturer. Available in pre-formed shapes and boards, foamed plastics are generally used in the low and lower intermediate service temperature range -182.8ºC to 148.9ºC (-297ºF to 300ºF). Consideration should be made for fire retardancy of the material.


Refractory fiber insulations are mineral or ceramic fibers, including alumina and silica, bound with extremely high temperature binders. The material is manufactured in blanket or rigid form. Thermal shock resistance is high. Temperature limits reach 1648.9ºC (3000ºF). The material is noncombustible.

The use and design of refractory range materials is an engineering art in its own right and is not treated fully in this manual, although some refractory products can be installed using application methods illustrated here.


Insulating and finishing cements are a mixture of various insulating fibers and binders with water and cement, to form a soft plastic mass for application on irregular surfaces. Insulation values are moderate. Cements may be applied to high temperature surfaces. Finishing cements or one-coat cements are used in the lower intermediate range and as a finish to other insulation applications. Check each manufacturer for shrinkage and adhesion properties.

All content copyright © 1996 - 2016 National Insulation Association.
12100 Sunset Hills Road, Suite 330 · Reston, VA 20190
(703) 464-6422 · fax (703) 464-5896
Trademarks and Terms of Use  PDF · Privacy Policy  PDF · Contact Us