Although closed-cell elastomeric foam insulation has been commercially available since the 1950s, some confusion still exists about the performance properties and benefits of this insulation type. That said, closed-cell elastomeric foam insulation has proven to be one of the top choices for cold (below-ambient) mechanical pipe and equipment applications.
The purpose of this post is to share some of the most common questions and concerns that we receive from building owners, engineers, and contractors.
What is Elastomeric Foam Insulation?
Essentially, elastomeric foam insulation is a synthetic rubber composed of a closed-cell structure available in factory-made tubes, sheets, or rolls. The outside edge consists of a smooth surface or “skin” which serves as a built-in vapor retarder.
Due to elastomeric foam’s flexible nature, it is less susceptible to cracks, breakage, and material loss when compared to rigid insulation options such as cellular glass, polyiso and phenolic foam. Finally, it’s also fiber-free and low-VOC for chemical emissions.
Alternative Names for Elastomeric Foam Insulation
It’s also known as closed-cell elastomeric foam insulation, flexible elastomeric cellular insulation, unicellular insulation, cellular elastomeric insulation, anti-sweat, refrigerant insulation, plumbing pipe insulation, refrigerant pipe insulation, HVAC pipe insulation and rubber insulation.
Typical Characteristics of Elastomeric Foam Insulation
Closed-cell elastomeric foam insulation is best known as an HVAC, refrigerant, and plumbing pipe or piping insulation because of its exceptional ability to control condensation on cold (below-ambient) mechanical systems.
Due to its low water vapor permeability, closed-cell structure, and built-in vapor retarder, elastomeric foam insulation is an excellent choice to protect piping and equipment from one of the most common problems and owner concerns in the building and construction industry – corrosion under insulation or “CUI”.
This is a costly, but preventable, problem when water, water vapor, or moisture penetrate the insulation and attack expensive mechanical systems.
When properly designed, specified, and installed, elastomeric foam insulation can effectively manage heat gain/loss and condensation control for the life of the mechanical system. Unlike open-cell fibrous insulation types, closed-cell foam does not lose its thermal efficiency or serve as a food source for mold growth when moisture comes in contact with the insulation.
One of the most important considerations when designing, specifying, and installing elastomeric foam insulation is the insulation thickness. Factors such as the fluid or gas (line) temperature in the pipe or equipment, pipe type, pipe size, ambient temperature, relative humidity, and whether or not a protective outer jacket will be applied are necessary to calculate the correct insulation thickness.
Elastomeric Foam Insulation Applications
Elastomeric foam insulation can be used in a wide range of applications, but the most common are:
- Refrigerant pipe insulation
- HVAC pipe insulation
- VRF (variable refrigerant flow) pipe insulation
- Chilled water pipe & equipment insulation
- Cryogenic pipe insulation (down to -297℉)
- Hot and cold domestic water pipe insulation (NBR/PVC up to 220℉, EPDM up to 257℉)
- Duct liner (fiber-free)
- Duct wrap
- Acoustic attenuation of pipes and ducts (lower frequencies)
- UV Exposure and Resistance
Regarding direct UV exposure, elastomeric foam insulation will degrade over time so it should be protected with the manufacturer’s specially-formulated UV coating or field-applied jacketing system. Traditional NBR/PVC (nitrile butadiene rubber/PVC) foam insulation will degrade faster than Aeroflex EPDM insulation; EPDM is inherently UV-resistant and will degrade at a slower rate than NBR/PVC.
Although not UV-proof, EPDM is the same type of rubber used for industrial and automotive applications. It’s also important to point out that the manufacturer’s white UV-protective coating meets national and state energy code requirements such as ASHRAE 90.1, International Energy Conservation Code® (IECC®), and California Title 24.
Fire Safety Requirements
American manufacturers of closed-cell elastomeric insulation must comply with ASTM manufacturing standards (ASTM C 534, C 411) and meet critical fire and smoke safety standards such as ASTM E 84 (UL 723) and NFPA 90A/90B.
Insulation that is plenum-rated is a term associated with meeting these fire safety standards which allows engineers to specify elastomeric foam insulation on pipes and ducts in air plenums. A plenum is generally the space between a structural ceiling (i.e. roof) and drops ceiling.
Currently, not all insulation types meet a flame/smoke index of ≤ 25/50 as referenced in ASTM E84 and UL723, while American-produced elastomeric insulation does up to 2” thick. This flame-retardant benefit can be a significant advantage in your project and may also be an essential part of meeting building code requirements. Not all applications require this flame/smoke index rating, but those that do will benefit from choosing elastomeric.
The International Mechanical Code (IMC) also requires that closed-cell elastomeric foam insulation be “listed” and “labeled”. This means that the manufacturer’s product must be listed on a 3rd-party test agency website, and ASTM E84 must be labeled on the manufacturer’s packaging.
All insulation types run some risk of moisture damage, but elastomeric insulation can prevent equipment damage more effectively than others. Elastomeric insulation has a water vapor permeability of 0.03 perm-inch and a closed-cell structure with a built-in vapor retarder that makes moisture damage less likely.
Its natural ability to repel moisture because of its closed-cell structure means reduced odds of moisture damage such as corrosion under insulation (CUI). One particular closed-cell elastomeric insulation is able to reach a water vapor permeability rating (wvt) of ≤ 0.01 perm-in that’s required in order to be considered officially water vapor retarder.
Elastomeric’s moisture-repelling abilities are significant enough that under ideal circumstances, additional vapor protection is not needed for this particular insulation type. However, this extra protection is a good idea—and may be necessary—in non-ideal circumstances, including cryogenic applications, and in extreme environments.
Closed-cell elastomeric insulation is also compatible with heat trace lines, for those interested in this method of preventing frozen pipes.
Limiting moisture damage goes a long way towards stopping mold growth, and elastomeric insulation’s closed-cell structure can help. Closed-cell insulation does not wick condensation due to its closed cell structure and built-in vapor retarder or smooth exterior skin.
This smooth exterior skin is easy to wipe clean, which is another step towards dirt and dust-free insulation. If nicked or dinged, the skin can be easily repaired with the manufacturer’s adhesive and/or flexible foam tape.
Open-cell fibrous insulation types, such as fiberglass, can unintentionally promote mold growth by wicking condensation. Once this condensation has been absorbed, it increases the spread of moisture inside the material itself, giving mold a foothold. Fibrous materials, or any insulation form that contains open-air pockets of any size, are also much more likely to trap dust and dirt.
Although they may seem like unlikely food sources, even dust and dirt can provide enough nutrients for mold to grow in the presence of moisture. Open-cell insulation types with vulnerable exteriors are at a greater risk for external damage, when not jacketed, that can surrender the inner structure to moisture-wicking due to constant vapor drive.
Closed-cell insulation is a superior insulation type in terms of condensation control, which is another proven method of preventing mold growth. Additionally, one closed-cell insulation manufacturer’s rubber is inherently microbial-resistant while others add a biocide during the manufacturing process.
Ninety-eight percent of moisture that condenses inside a typical building cavity permeates from the outdoors by an air leakage mechanism. Using a closed-cell insulation type will cut effectively manage condensation that can soon give way to mold.
Making an effort to prevent mold can go a long way towards reducing instances of asthma, allergies, and similar medical conditions while providing healthy indoor air quality (IAQ) for building occupants.
Addressing HVAC Background Noise with Closed-Cell Elastomeric Foam Insulation
While closed-cell elastomeric foam insulation is most often considered for refrigerant piping applications, it can deliver specific acoustic performance benefits for HVAC duct applications.
The ductwork in commercial and industrial buildings, such as civic, education, government, healthcare, high-tech, manufacturing, office, and religious are most often wrapped with standard open-cell fibrous duct wrap for energy efficiency. When owner project requirements (OPR’s) require certain occupant spaces to meet acoustic performance (i.e. classrooms), duct liner can deliver energy efficiency, condensation control, and acoustic attenuation.
Most duct liners that are specified and installed are composed of open-cell fibrous materials with added biocides and protected surfaces facing the airstream to prevent fibers from breaking away and being released downstream into occupant spaces. Open-cell is the go-to duct liner for a few reasons – low cost, acoustic attenuation at higher frequencies, and installation cost.
When OPR’s identify the specific acoustic performance of HVAC ductwork to reduce background noise, and first-cost is not the number one requirement, an acoustic engineer may become a member of the project design team to identify materials and systems to meet the project team’s basis of design (BOD).
Acoustic engineers often consider and evaluate duct insulation (wrap or liner) to address HVAC background noise. They utilize data from manufacturer acoustic test reports and input it into their software to evaluate the sound absorption qualities of different insulation materials.
One well-known test method is ASTM C 423 Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method. This test essentially reports the sound absorption performance of materials, in a range of octave bands from 100 Hz to 5000 Hz, as they correlate to reverberation times in an occupant space.
With the ASTM C 423 standard, absorption coefficients are documented at various frequencies and averaged to assign a noise reduction coefficient (NRC, reported as 0-1.0) to the tested material. While it is a fact that open-cell fibrous duct insulation attenuates sound at higher frequencies (above 1000 Hz, NRC average = .70), it’s the lower frequencies (500 Hz and below) that can be problematic with regard to HVAC background noise.
Closed-cell elastomeric foam duct wrap and duct liner insulation effectively attenuate airborne and structure-borne sound originating from HVAC ductwork, such as fan noise and sheet metal vibration, in the 250 Hz to 500 Hz range.
Additionally, closed-cell elastomeric foam duct insulation offers the following performance benefits:
- Always fiber-free
- Closed-cell structure efficiently controls condensation
- Will not wick moisture if punctured
- Smooth skin facing air stream is easy-to-maintain
- Microbial-resistant (alternative to UV light)
- Low-emitting for chemical emissions (3rd-party certified)
- LEED® compliant
Other factors to consider when comparing to traditional duct insulation include:
- Higher cost (material and installation)
- Weight (3.0-6.0 lbs./ft3)
- Should be protected from UV light
Closed-cell elastomeric foam HVAC duct insulation is certainly not suitable for every project. However, it can address specific HVAC background noise concerns for project design teams and building owners. When compared to other acoustic equipment options, closed-cell elastomeric foam HVAC duct wrap and liner insulation can offer favorable first and lifecycle costs to building owners.
Acoustic Qualities of Elastomeric Foam Insulation
Closed-cell elastomeric foam insulation is not commonly considered for acoustical applications. While open-cell insulation materials attenuate sound at higher frequencies, closed-cell elastomeric foam insulation can address problematic building mechanical system noise generally at lower frequencies in the 250Hz-500Hz range. Common applications include fiber-free duct liner, duct wrap, and pipe covering.
The Energy-Saving Qualities of Closed Cell Elastomeric Foam Insulation
Every building owner wants to own a building with an energy-efficient mechanical system (HVAC, refrigeration, and plumbing). However, their cost of ownership can be compromised by incorrect material selection, improper insulation thickness, value engineering, improper installation, and the absence of a maintenance plan.
Energy is a primary cost of building ownership that impacts profitability, LEED® certification, leasing/rental rates, and marketability. Mechanical insulation provides a favorable return on investment to building owners because their investment saves a measurable amount of energy in a relatively short period of time.
While there are numerous mechanical insulation types to choose from, professional mechanical engineers and design-build contractors are knowledgeable about the best insulation choices to meet their owner’s project requirements (OPR’s). They must analyze factors such as system operating temperature(s), ambient temperature ranges, operating environment (interior/exterior), code compliance, sustainability, material/labor costs, and more.
Closed-cell elastomeric foam pipe and duct insulation is often specified and installed on below-ambient (cold) systems because it’s thermally efficient and effectively manages the inevitable effect of condensation on cold operating systems. Because of its closed-cell structure and built-in vapor retarder, closed-cell elastomeric foam does not require a vapor retarder or jacket unless it is intended for an extreme operating environment or will be exposed to UV and/or mechanical damage.
Flexible elastomeric foam insulation results in a favorable life cycle cost to owners because a supplemental vapor retarder is not required and maintenance costs can be minimized. Assuming that the correct insulation thickness is calculated for condensation control and all seams are properly sealed, closed-cell elastomeric foam insulation does not lose its thermal efficiency (energy loss) when exposed to moisture or light damage to the exterior skin.
Because of its closed-cell structure, the interior of the insulation does not “wick” moisture through the insulation system. A ding can be easily repaired with adhesive and tape. This physical characteristic prevents energy loss, mold growth, water damage, and decreased maintenance costs.
There are American-made choices available to building owners when it comes to closed-cell elastomeric foam. However, only Aeroflex USA’s Aerocel® brand of EPDM (ethylene propylene diene monomer) closed-cell elastomeric foam insulation is hydrophobic. EPDM’s chemical structure differs from NBR/PVC products because EPDM does not induce or react to water vapor.
In other words, EPDM naturally resists moisture in its environment. Additionally, EPDM is naturally microbial-resistant so EPA-registered biocides are not added during manufacturing. These are just a few of the reasons why motor vehicle manufacturers choose EPDM rubber for durability of components such as wipers, seals, hose, belts, wire cable covers and more.
Aerocel® closed-cell flexible elastomeric foam pipe and duct insulation save energy and provide building owners with a favorable cost of ownership for their building mechanical systems.
Ease of Installation
Closed-cell elastomeric insulation is relatively easy to install because it’s easy to cut, apply and seal on the job site. A separate fabrication step is not required. Since it’s lightweight and flexible, time and breakage/material loss are minimized.
Manufacturers offer time-saving and quality solutions such as “self-seal” tubes, specially-formulated special-purpose contact adhesives, protective coatings, insulated pipe hanger fittings, factory-fabricated fittings, and tapes to help achieve quality installation outcomes.
U.S. manufacturers of closed-cell elastomeric foam offer tubes in standard unslit or self-seal formats. Sheets and rolls are also offered with or without a factory-applied pressure-sensitive adhesive (PSA) on one side. Self-seal tubes and sheets/rolls with PSA offers are known to deliver significant labor savings during installation.
Tubes are generally available in “wall thicknesses” of ¼” to 2” and inside diameter (ID) sizes of ¼” to 6” IPS (iron pipe size). Aeroflex offers tube sizes up to 16” IPS. Sheet sizes are typically 3’x4’ and rolls 48” wide with thicknesses ranging from ¼” to 2”.
Closed Cell Elastomeric Foam Insulation is SAFE
Mechanical insulation, the type installed on building mechanical systems such as HVAC, refrigeration, and plumbing equipment, delivers one of the quickest returns on investment to building owners when compared to all other building materials. Performance benefits include fire-safety, energy efficiency/savings, healthy air quality, thermal comfort, acoustic attenuation, and contributions to LEED® certification.
However, building owners and mechanical engineers continue to justifiably maintain concerns about the potential negative performance impacts of mechanical insulation. Such concerns include harmful material ingredients such as formaldehyde and fibers, moisture-wicking when subjected to moisture, the potential for mold growth, and decreased thermal performance.
Closed-cell elastomeric foam pipe and duct insulation are SAFE due to their inherent ability to manage many of the human health concerns mentioned above.
- Passes ASTM E84 25/50 (fire/smoke safety)
- Low thermal conductivity (energy efficiency, thermal comfort)
- Efficiently controls condensation due to its closed-cell structure and built-in vapor retarder (energy efficiency, mold management)
- Formaldehyde, fiber, and PBDE-free
- Low-emitting material for chemical emissions (3rd-party certified)
- Low-VOC adhesives & coatings
- Attenuates lower frequency noise (i.e. fans, sheet metal vibration/rumble)
Most available closed-cell flexible elastomeric foam insulation is manufactured with a nitrile butadiene rubber and PVC (NBR/PVC) base. Aeroflex USA’s Aerocel® brand of closed-cell elastomeric foam pipe and duct insulation is manufactured with an EPDM rubber which offers several additional performance benefits:
- Hydrophobic (does not induce or react to moisture)
- Upper continuous service temperature of 257°F
- No biocides added (EPDM is naturally microbial-resistant)
- Greater durability to UV exposure
Wrapping it Up
Closed-cell elastomeric insulation offers a wide range of benefits, particularly in terms of condensation control and mold prevention.
In most instances, choosing closed-cell elastomeric insulation will provide a favorable life cycle cost for building owners by delivering thermal efficiency, condensation control, low-VOC emissions, mold management, acoustic attenuation, and thermal comfort to help facilitate a safe and productive work environment for building occupants.
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