Cellular Glass: Achieving an Environmental Balance

July 1, 1998

Specifiers of construction materials find themselves on the front

line of today’s environmental struggles. They need to know all the

implications of their product selections, both short and long-term.

While insulation materials constitute a relatively small part of

the overall cost of a building or plant, they determine a

disproportionately large share of a facility’s long-term

environmental impact.

For purposes of this discussion, the environmental impact of

thermal insulation falls into two categories: indirect and direct.

Indirect environmental impacts are those which reduce the amount of

energy consumed or lost through inferior or inadequate insulation.

Reducing energy losses reduces the demand for energy, thereby

conserving nonrenewable fuel supplies and reducing the amount of

pollutants, such as carbon dioxide (CO2) , sulfur dioxide (SO2) and

nitrogen oxides (NOx), released into the atmosphere through the

burning of fossil fuels.

Direct environmental impacts result from the insulation

manufacturing process itself, like the release of

chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) and

other potential ozone-depleting foaming agents, as well as from the

landfill disposal of spent insulation.


Most of the world’s environmental problems, including pollution,

ozone depletion, acid rain, global warming and waste disposal, can

be tied in one form or another to energy consumption.

Pollution Thermal insulation plays a significant role in both the

consumption and conservation of energy. The reduction of energy

demand through the use of energy-efficient construction practices

and insulation ultimately will reduce pollution from the burning of

fossil fuels for direct heating and generation of electricity.

Ozone Depletion According to the U.S. Environmental Protection

Agency (EPA), a major use of HCFCs and other chemical foaming

agents in the United States is for the manufacture of plastic

insulating foams, including polystyrenes, phenolics, polyurethanes

and polyisocyanurates.

Acid Rain There are two ways to minimize acid rain formation: (1)

burn less fossil fuels; and, (2) remove the SO2 and NOx from the

combustion gases. Reducing energy demand and the burning of fossil

fuels by using energy-efficient building practices and insulation

to decrease will also have a positive carry-over affect on the acid

rain problem.

Global Warming The only realistic means of reducing production of

greenhouse gases is through the control of ozone-depleting agents.

Waste Disposal When designing and constructing buildings and

plants, careful attention must be paid to both the environmental

and economic life cycles of the insulation system. Both the

manufacture of building materials and the construction of buildings

and plants consume considerable amounts of energy. Specifiers of

building materials and construction practices need to ensure that

they are selecting efficiently manufactured materials, which will

provide maximum service life before needing to be replaced and


By specifying and using insulation with a long life expectancy,

companies save not only money on replacements and retrofits, but

also ensure they are doing their part to reduce the waste stream.


When selecting an environmentally responsible insulation, it is no

longer sufficient merely to select the required R-value. The

insulation must also (1) provide constant energy savings, (2) be

environmentally benign during manufacturing, (3) have a service

life that will ensure long-term performance and minimize

replacement and disposal in landfills, and (4) pose no health risks

to those handling or installing it.

Realistically, these concerns need to be balanced with concerns

of cost-effectiveness. The energy cost-effectiveness of an

insulation can be expressed in terms of cost savings. If the cost

of the energy saved by using a particular insulation is less than

the total energy used in its manufacturing, installation, planned

use, plus the energy used to recycle it, then it is not cost-

effective. Also, the amount or cost of pollution avoided by using

a certain type of insulation throughout its service life should be

greater than the cost of pollution resulting from its manufacture

and use. By carefully weighing all the factors and costs involved

in these two relationships, the overall environmental profile of an

insulation, or its “Environmental Balance” can be determined.


The following critical concepts should be kept in mind when

selecting an environmentally responsible thermal insulation. An

insulation’s energy cost effectiveness might be expressed in terms

of energy cost savings. If the cost of the energy saved by using a

particular insulation is less than the total energy used in its

manufacturing, plus that used to recycle it, then it is not cost

effective. This relationship can be expressed as follows:

Energy Cost-Effectiveness =



(Energy Saved)


(Manufacturing Energy + Recycled Energy)


(If > 1.0, it is cost effective; if < 1.0, it's not.)

The amount or cost of pollution avoided by using a certain type of

insulation throughout its service life should be greater that the

cost of pollution resulting from its use. The pollution reduction

effectiveness of an insulation can therefore be expressed as


Pollution Reduction Effectivenes =



Pollution Cost Savings


Actual Pollution Costs


(If > 1.0, it is an effective anti pollutant; if < 1.0, it's not.)

By carefully weighing all the factors and costs involved in the

above two relationships, a particular insulation’s overall

environmental profile or Environmental Balance can be determined.

It can be expressed as follows:

Environmental Balance =


Energy Cost-Effectiveness

+ Pollution Reduction Effectiveness


(If > 2.0 excellent; between 1.0 & 2.0 good; if < 1.0 poor.)

The above relationships hold true only if the insulation is (1)

used in the proper way, (2) used in the correct thickness, (3) is

properly installed, and (4) it maintains its expected performance

and physical properties throughout its entire service life.


In discussing how insulation achieves environmental balance, three

critical attributes of the product must be evaluated: (1) its

environmental profile, (2) its service life and efficiency, and (3)

its environmental cost-effectiveness.

The environmental profile of an insulation depends on the following

four characteristics: (1) its raw materials; (2) its manufacturing

process, including gray energy, or, the energy expended during the

extraction, processing and transportation of raw materials; (3)

installation and related methods and materials; and, (4) its



The Manufacturing Process insulation consists exclusively of minute

sealed glass cells, formed through chemically reacting finely-

ground oxidized glass with carbon at a high temperature. All the

raw materials used to make glass are naturally occurring

substances, commonly found in nature. None constitute a danger to

man or the environment.

The manufacturing of cellular glass insulation involves the

production of glass and a foaming (cellulating) process. This

process produces CO2, which becomes entrapped in the tiny glass

cells of the material. No additional foaming agents, HCFCs,

organic binders or potentially harmful substances are used that

might contribute to atmospheric pollution. In the finishing stage,

rough blocks of cellular glass are cut and trimmed to their desired

dimensions. During finishing, a certain amount of crushed glass or

glass dust is produced as well as a small quantity of hydrogen

sulfide (H2S). The glass dust is relatively heavy, so it is

classified as a nuisance dust. It is neither carcinogenic nor

likely to cause silicosis. Almost all of the dust and glass scraps

are collected and recycled in a melting furnace to make new glass.

Energy Use & Air Pollution Manufacturing of cellular glass

insulation is essentially a thermal process and uses considerable

energy, from both electrical and natural gas heating, to melt and

foam the glass. While heating with natural gas and generating

electricity with fossil fuels mean releasing air pollutants, the

pollution resulting from manufacturing is considerably less than

would result from increased energy use if cellular glass insulation

were not used.

Plant Energy Efficiency The plant recovers energy from both of its

most energy intensive operations: glass melting and cellulating.

In both operations, hot exhaust gases from the combustion of

natural gas are used to preheat the air used in the combustion


Installation and Use The cutting and fitting required during the

installation of cellular glass insulation and related accessory

materials releases small quantities of entrapped gases (CO2, CO and

H2S) that might otherwise be considered harmful to the environment.

However, the quantities are too small even to be considered

atmospheric pollutants.

Disposal Because of the unique physical characteristics of

cellular glass insulation, it has a long service life. Typically,

the system on which the insulation is installed is replaced before

the insulation reaches the end of its life, or the site where it is

installed is demolished. When the insulation reaches the disposal

stage, will it have a detrimental impact on the environment?

Although all of the physical insulating properties of cellular

glass insulation are usually intact at the time of removal or

building demolition, it is not feasible to reuse this material as

an insulation. The time required to salvage, sort, clean, etc.,

would be economically prohibitive. Crushed cellular glass,

however, can be used as a fill material for roadways and as a

supplement to asphalt paving.

In most instances, cellular glass insulation ends its product

life in either a municipal landfill or in a construction-and-

demolition landfill. Crushing the insulation prior to disposal

reduces its volume by 5-7 times. Since it is inert and

environmentally benign, there is no danger to the ground water



While it’s possible to construct facilities to last 50 years or

more, construction practices today are turning out structures with

as little as a 20-year service life. The unusual composition of

insulation makes it uniquely resistant to all types of normal

insulation damage, including moisture absorption, thermal expansion

and contraction, fire, corrosion and vermin. Because of its long-

lived insulating properties, cellular glass insulation may even

extend the service life of a facility.

The environmental “bottom line” of any insulation is how much

energy pollution it saves or avoids through its use. In

calculating two scenarios using a particular brand of cellular

glass, we find that (1) by installing 2-inch-thick insulation on a

12-inch steam line operating at 400 F per 100 sq. ft. of pipe

surface, the energy pollution saved over a five-year period by

using the insulation equals 1,900 times the amount of energy as the

energy pollution created during the manufacture of the insulation;

and, (2) the energy saved by installing 4-inch-thick cellular glass

insulation per 1,000 sq. ft. of roof area over a 40-year life is

134 times of the energy-pollution created during the manufacture of

the insulation.

The Pittsburgh Corning -proposed decision-making process for

selecting cellular glass insulation involves three separate

evaluations, each assigned its own weight or number of points:

technical, economic and environmental. Out sales representatives

and engineers routinely assist in deciding which insulation

materials and systems are best or a particular application.


In conclusion, the environmental crises we are confronting today

cause us to re-evaluate the building practices of the last several

decades. No longer can we afford to be energy-inefficient or

environmentally unwise.

In order to make educated decisions about the environmental

characteristics and performance of any insulation product, contact

the manufacturer directly. Building materials, including

insulation, need to be environmentally safe during their

manufacture, installation, service life and disposal. In

additional, constructing buildings and facilities using energy-

efficient materials and methods to provide a service life of at

least 30 to 50 years is the only way we can achieve a level of

economic and environmental cost-effectiveness acceptable to

businesses, consumers and the community at large.