polyisocyanurate vs. cellular glass insulation

Customer Bulletin 0610 June 2010

CUSTOMER BULLETIN 06-10

POLYISOCYANURATE VS. CELLULAR GLASS INSULATION

PURPOSE

This Customer Bulletin is another in our series of white papers aimed at providing our clients,

engineers, contractors, fabricators, and friends with objective information on our products and

those of our competitors. This Bulletin focuses on a comparison of the physical properties of

closed cell polyisocyanurate (PIR or polyiso) rigid foam insulation with those of cellular glass

insulation for below ambient applications such as chilled water through cryogenic application

where moisture intrusion or condensation can be an issue.

Dyplast’s ISO-C1®1

polyiso and Pittsburgh-Corning’s FOAMGLAS® 2 were selected for

comparison since they were each judged best-in-class.

The result of the comparison was that ISO-C1 is the ideal choice for applications ranging from

minus 297°F up to plus 300°F service temperature - - such as chilled water, refrigeration,

HVAC, domestic hot and cold water and cryogenic applications. Note that while this Bulletin is

focused on differences between FOAMGLAS and ISO-C1, there are indeed differences between

the physical properties and performance characteristics of competing PIR insulations. We

recommend end-users view other Customer Bulletins from Dyplast that address these

differences.

SUMMARY

K-factor: The aged thermal conductivity (k-factor) at 75°F of ISO-C1 polyiso is 0.176

Btu·in/hr·ft2·°F whereas FOAMGLAS brand cellular glass is 0.29. Thus the thermal

insulation performance of cellular glass is roughly 65% worse than polyiso, which results in

cellular glass insulation systems being much thicker (important from a weight, cost, and space

aspect).

Brittleness: Cellular glass is susceptible to vibration, movement, thermal shock, and mechanical

shock. Cellular glass may be unsuitable for application in process environments with high

vibration, movement, or thermal/mechanical shock. During installation, if cellular glass is

dropped it may shatter; also if metal banding is applied to tightly cell glass can break, or if

banding has a coefficient of expansion different than cell glass it could crack the insulation

during a thermal cycle. If cellular glass breaks the cracks may create a path for heat and/or

1 ISO-C1 is a registered trademark of Dyplast Products, LLC; a usage of ISO-C1 without the ® symbol is not

intended indicate any relinquishment of Trademark Rights

2 FOAMGLAS, PITTCOTE, and PITTWRAP are a registered trademark of Pittsburgh-Corning Corporation; a usage

of any Mark without the ® symbol is not intended indicate a relinquishment of Trademark Rights


moisture to pass, thus compromising the insulation system; whereas polyiso is not brittle and

is not as susceptible to vibration, movement, or thermal/mechanical shock. When ISO-C1 is

installed in areas where mechanical abuse is expected (such as workers stepping on the

insulation), higher density polyiso with its higher compressive strengths may be considered.

Even when abused, normal 2.0 lb/ft3 density polyiso is not brittle and it does not crack or

shatter like cellular glass. Cellular glass is even prone to damage during shipping and handling

unless packaged in suitable cartons with spacers, whereas polyiso can be thrown into poly

bags and shipped with minimal damage, thus materially reducing packaging and shipping

costs, and related waste.

Water Absorption: Measurement per ASTM C272 (Method A), which requires a 24 hour

immersion period, demonstrates ISO-C1 (2 lb/ft3 density) has a 0.04% by volume water

absorption. The comparable FOAMGLAS test per ASTM C240 requires only a 2 hour

immersion, and the FOAMGLAS results are 0.2% by volume. Thus it is clear that

FOAMGLAS has no advantage in water absorption.

Installation – the “insulation system”: A particular insulation product can perform at its peak

only when properly installed within a more complete “insulation system” with sealants,

adhesives, vapor barriers, mastics, jacketing, and so forth. A cellular glass insulation system is

generally more complex than a comparable polyiso insulation system and thus is more labor-

intensive to install - - with the result that there is more potential for errors during the

installation process. For example:

Since the lengths and diameters of FOAMGLAS insulation segments are smaller than those of

polyiso (18”x24”x7” maximum), there will be more segments (pieces) of FOAMGLAS to

install as compared to a polyiso system. Even for small-bore pipe, FOAMGLAS will be

delivered in maximum 2-foot sections, while ISO-C1 is typically fabricated in 3-foot sections

(and could conceivably be longer). More pieces and parts means more seams and joints to

seal, which means more labor, more consumption of materials, and more possibility of

improper installation (e.g. a seam not sealed, or a cracked piece of insulation) - - which can

lead to thermal and/or moisture leaks. A FOAMGLAS insulation system is also likely to have

more layers than a comparable polyiso system thus requiring more steps in the process, more

joints to seal, and resulting in more consumption of sealants, tapes, adhesives, etc.;

According to manufacturer’s installation recommendations, a typical FOAMGLAS system in

a low temperature application may require a coat of mastic (3 to 4 gal./100 ft2 either sprayed

or trowelled), then a layer of synthetic mesh fabric, and then a second coat of mastic. An

ISO-C1 system installation, on the other hand, requires only a vapor barrier sheeting applied

over the insulation - - and this could actually be shop applied, making field assembly even

easier;

Bore Coatings may be required where FOAMGLAS abrasion may erode the pipe;

Mixing of 2-component adhesives require extra steps and time, and may contain carcinogens

that require special ventilation or other respiratory protection;


Although ISO-C1 and FOAMGLAS both generate dust during fabrication or in-field shaping,

cellular glass is considered particularly problematic, and sometime vacuuming is suggested in

FOAMGLAS installation instructions.

Weight: FOAMGLAS can vary in density but typically is supplied at 7.5 lb/ft3

- - a density

close to 4 times that of 2 lb/ft3 polyiso. The low thermal efficiency of cellular glass (65%

worse than polyiso) compounds the problem since cellular glass installations may require

almost double the thickness. The result is a major increase in weight and volume on a given

pipe run. [For example assume a 12” diameter run of piping requiring 4” of polyiso insulation

at 2 lb/ft3 density; every linear foot of insulation would weigh 2.8 lbs; even ignoring humidity,

wind, etc. 6.6 inches of cellular glass must be applied to achieve the same R-value, resulting

in the weight of a linear foot of cell glass approaching 20 lbs per linear foot- - 7 times more

weight than polyiso]. The costs of additional pipe hangars, stress on joints that can lead to

failure, and inability to run multiple pipes in a small space make cellular glass a challenging

insulation.

Size of insulation blocks/segments: Polyiso bunstock is manufactured as large continuous

“buns”. ISO-C1 bunstock production equipment can be adjusted to produce variable block

dimensions depending on particular customer needs. Bun widths for a nominal 2 lb/ft3 density

can vary from a trimmed 38 inches up to a trimmed 52 inches, with standard sizes set at 48

inches. Bun lengths can vary from 36 inches (standard pipe chunks) up to 288 inches. The

bun heights for other ISO-C1 densities will vary. The largest FOAMGLAS blocks are

produced with dimensions 18 x 24 x 7 inches. The smaller dimensions will limit the size of

the pipe insulation segments, thus requiring more segments to insulate pipe, and more

seams/joints.

Vapor Barriers: Vapor drive is increasingly a major problem at lower process temperatures.

From refrigerant to cryogenic temperatures vapor drive can be severe and lead to failure of the

insulation system without a properly installed vapor barrier system. FOAMGLAS advertises a

water vapor transmission of “0” perm-inch per ASTM E96. ISO-C1 has excellent WVT at

1.65 perm-inch, yet not zero. Engineers and end-users, however, agree that the permeability of

the fully-installed insulation system is the ultimate objective - - while mitigating life-cycle

permeability risks created by poor installation, joint failures, mechanical abuse, thermal

cycling, degradation of material performance over time, etc. ISO-C1 installations have fewer

pieces/parts, fewer joints, are less susceptibility to cracking/shattering, and have excellent life-

time performance.

In all low-temperature pipe and equipment insulations, both FOAMGLAS and ISO-C1

installation guidelines indicate a vapor barrier should installed over the insulation. ISO-C1

installation guidelines are consistent with other polyiso manufacturers, engineers, and

contractors, recommending a properly installed zero-perm vapor barrier wrap over lengths of

pipe (which can be factory-applied or field-applied). Installation guidelines for FOAMGLAS

recommend, depending on the application, either a vapor retarder mastic (sometimes in 2

trowelled/sprayed layers with mesh in between) or a vapor retarder wrap - - unless conditions

are “mild below ambient” where a 2-layer weather barrier mastic or even a metal jacket

without mastic is deemed adequate. We would caution end-users to consult their insulation


engineer. Note also that the manufacturer of FOAMGLAS states that with an “asphalt bonded

fabrication, with all joints of the outermost layer of FOAMGLAS insulation completely sealed

and drawn tight, the system is vapor sealed and no additional vapor barrier is required”. End-

users should be aware, however, that asphalt bonding can not be used in many lower

temperature applications, and end-users should be cautious of having no backup vapor barrier

available if a joint opens or crack appears.

Jacketing: ISO-C1 installation guidelines are again consistent with major engineering

companies and insulation contractors, generally recommending a metal jacket to protect the

insulation system from mechanical abuse and weather-related insult/wear. PVC jacketing may

be appropriate when frequent wash-downs or FDA cleanliness requirements dictate. Yet end-

users should note that an ISO-C1 insulation system, similar to FOAMGLAS systems, can

perform well without a jacket if mechanical abuse or weather is not a problem. FOAMGLAS

installation guidelines also require a metal jacket in all cases where the insulation system will

be exposed to ultraviolet light.

Combustibility and Flame/Smoke: Although cellular glass is advertised as having a zero flame

spread index (FSI) and a zero smoke developed index (SDI) per ASTM E84 testing, either the

recommended vapor retarders, weather barriers, sealants, mesh, or adhesives typically

specified with cellular glass may be flammable or prone to emit smoke during fires. For

example both PITTCOTE® 300 (asphalt mastic), PITTWRAP

® CW300 (non-metallic jacket),

and PC® product data sheets indicate they are combustible. [Note that some liquid products

may be combustible while they are being applied, yet may not be after they have cured]. Note

also that cellular glass can shatter and lose its insulating integrity when thermally shocked.

Although ISO-C1 has a 25/130 FSI/SDI rating at a thickness of 4 inches, when exposed to

flame, ISO-C1 insulation will char yet maintain its shape long enough to provide precious

minutes of thermal protection to pipe, equipment, and vessels to allow response.

[Important Note: Section 602.2.1 of the International Mechanical Code states

that materials within return air plenums shall be either non-combustible or

have a 25/50 fire spread index and developed smoke index when tested in

accordance with ASTM E84. Interpretations by other code authorities have

allow compliance with NFPA 255 or UL 723 as substitutes for ASTM E84.

Essentially this means that insulation systems (and all accessory

components within, such as sealants, vapor barriers, etc.) installed in either

air plenums or inhabited areas to be non-combustible or ≤ 25/50. Name-

brand cellular glass such as FOAMGLAS meets this 25/50 requirement.

ISO-C1 polyiso is 25/130, so it should not be installed in air plenums or in

indoor inhabited areas. Caution should be observed that when using

cellular glass in such applications that all related sealants, barriers, and

such are ≤ 25/50.]


WVT (Water Vapor Transmission, or permeability): ISO-C1 has excellent WVT at 1.65 perm-

inch, yet not zero as advertised for FOAMGLAS. Engineers, contractors, and end-users

generally contend, however, that it is more important to consider the permeability of the entire

installed insulation system. The greater number of joints, added complexity of installation that

can lead to mistakes, propensity for shattering, short life-time performance of sealants and

adhesives, and so forth can override any intrinsic permeability of FOAMGLAS. On the other

hand, ISO-C1 is easily installed with a zero-perm vapor barrier that can be either factory-

applied or field-applied. The final installed system generally has fewer joints than a similar

cellular glass system, and is less prone to failure.

Cost: The material costs of ISO-C1 are roughly half that of FOAMGLAS. Considering the

additional costs associated with the installation of cellular glass (both labor and pieces/parts),

the overall installed cost of cellular glass can easily be 3 or more times expensive than

polyiso; life-cycle costs relating to energy loss and maintenance also will favor polyiso over

cellular glass.

Chemical resistance: Cellular glass is often advertised as being impervious to chemicals and is

indeed resistant to organic solvents and nearly all acids. Yet polyiso insulation can be used to

insulate piping and vessels containing almost any material, and is suitable for use where

incidental contact with most solvents and chemicals is possible.

Compressive strength: Cellular glass indeed has high compressive strength commensurate with

its weight and brittleness. Yet ISO-C1 polyiso insulation is available in compressive strengths

exceeding 125 psi, more than adequate for the vast majority of applications (e.g. pipe hangars

and areas of mechanical abuse) - - while delivering thermal performance vastly superior to

cellular glass - - and with fewer problems associated with cracking and weight management

(see sections on brittleness and weight).

Coefficient of Linear Thermal Expansion (CLTE): Cellular glass has a CLTE close to that of

carbon steel, and thus requires fewer contraction/expansion joints than a polyiso insulation

system. More expansion joints would be required for aluminum, copper, nickel, their alloys,

and austenitic stainless steel piping. Polyiso, however, is easier to work in the field and

polyiso contraction/expansion joints are relatively easy to install.

Dimensional Stability: Dimensional stability is a combination of both reversible and irreversible

changes in linear and volumetric dimensions. FOAMGLAS product data sheets advertise

excellent to extraordinary dimensional stability, yet ISO-C1 insulations also have very good to

excellent characteristics. The bottom line is that with properly installed

contractions/expansion joints the issue is mute since any temporary or permanent changes in

dimension can be accommodated by insulation system design. Note that some cellular glass

manufacturers make comparisons against polyurethane insulation without noting that

polyisocyanurate is a different chemical formulation with much improved dimensional

stability; note also that ISO-C1 has the best dimensional stability when compared with

competitive polyiso products.

Safety: The MSDS sheets of each product utilized within any insulation system should be

reviewed for potential hazards. Also, jobsites should of course establish and enforce prudent


safety practices. A review of product data sheets and MSDS literature for both ISO-C1 and

FOAMGLAS lead to a conclusion that FOAMGLASs and related materials required for

insulation represent more hazards relating to carcinogens, combustible compounds (during

storage and usage), dust, abrasion, and weight than those in a comparable ISO-C1 installation.

Maintenance: All insulation systems should be part of the preventive maintenance system,

checking not only for damage or deterioration, but ensuring re-installation after maintenance

on insulated equipment. Insulation systems are generally compromised either by:

1. Mechanical abuse, such as personnel stepping on insulation or vehicles bumping into

insulation; such abuse can dislodge jackets, puncture vapor barriers, open sealed seams

between insulation segments, or crush insulation; ISO-C1 and FOAMGLAS are equally

susceptible to such damage, with certain exceptions; while FOAMGLAS may have

higher compressive strengths at its “standard” density, when the compressive limits are

exceeded FOAMGLAS shatters and loses virtually all its thermal integrity; ISO-C1 on

the other hand has more resilience, and even when deformed it will maintain some of its

original performance;

2. Thermal shock, when severe, can crack or shatter FOAMGLAS, whereas ISO-C1 is not

as susceptible to thermal shock;

3. Weather can result in deterioration of an insulation system in several ways; although rain

alone should not be a factor, extreme winds can dislodge jacketing and can then pummel

vapor barriers with wind/rain - - creating or exposing defects; UV radiation can degrade

materials; although the elements of an ISO-C1 system and FOAMGLAS system are each

somewhat susceptible, an ISO-C1 system may have the advantage by virtue of fewer

joints, seams, and overall size;

4. Deterioration of materials is an important factor since some compounds used in the

installation of FOAMGLAS may have a lifetime of 10 or so years; in such case, the

performance of a sealant or mastic may be compromised.

The following table displays key physical properties of polyiso (ISO-C1) and cellular

glass(FOAMGLAS). Note that these are “product” values, and not “insulation system”

values.

Insulation Material Units ISO-C1 FOAMGLAS

Thermal (at 75°F) k-factor (aged) 0.176 0.29

WVT Perm-inch 1.65 0.00

Flammability ASTM E84 rating (4 in.thick) FSI/SDI 25/130 <25/50

Density lb/ft3 2.0 7.5

Water Absorption % by volume 0.043 0.2

4

3 As measured in a 24-hour test per ASTM C272

4 As measured in a 2-hour test per ASTM C240


Qualitative Comparison Chart:

Quality ISO-C1 FOAMGLAS

Thermal Performance Excellent Fair

WVT without vapor barriers Very good Excellent

WVT with vapor barriers Excellent Excellent

Available with factory-applied

vapor barrier

Yes Possibly, for smaller sizes

Closed cell structure Yes Yes

Fiber free Yes Yes

Non-porous Yes Yes

Mold resistant Yes Yes

Very Resistant to

vibration/movement

Yes No

Recommends a jacket Yes For most applications

Thicknesses available Virtually unlimited,

from 1/2” upwards

Limited, 1” minimum

Lengths Virtually any Sold in 2 foot maximum

polyisocyanurate vs. cellular glass insulation

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