Advances in Flexible Closed Cell Insulation Products for Specific end use Applications

Roger Schmidt

August 1, 2001

Flexible elastomeric closed cell insulation products have been in the market place for nearly fifty years. Like most mature products, product modifications for specific applications occur as the technology advances and markets change. Many of these modifications have really entered the market place in just the past five years. This article addresses five of these product modifications.

  • Flexible Elastomeric Insulation with Pre-Applied PSA (Pressure Sensitive Adhesives)

  • Non-Black Elastomeric Insulation
  • Non-Halogen Elastomeric Insulation
  • High Temperature Resistant Products
  • Non 25/50 Rated Applications
Flexible Elastomeric Insulation with Pre-Applied PSA (Pressure Sensitive Adhesives)

Easier to use products are driving forces in today’s markets. Elastomeric insulation has been traditionally installed using solvent-based contact adhesives. This is still the predominate method of installation. However, because of the need for easier/faster product application methods, elastomeric insulation (tubular, sheets and roll form) is now available with pre-applied pressure sensitive adhesives (PSA). The technology of pressure sensitive adhesives has greatly improved in recent years to the point where tearing of the rubber substrate will occur. Testing of adhesives indicates that good adhesion is found where the material fails before the adhesive. The PSA applied products offer the following advantages:

  • Reduce odor, material waste, and use of potentially hazardous materials at the job site

  • Ensure complete and uniform coverage of adhesive
  • Have excellent adhesion to most substrates
  • Require no special tools for application
  • Can be installed more quickly
  • Clean up faster
  • Have better appearance

Tubular elastomeric insulation with pre-applied PSA is ideal for straight pipe runs where the longitudinal seams can be sealed, simply by pressing them together. Contact adhesive is still required for the butt joints. For pipe runs with tight bends or sections with numerous fittings, the non-slit standard insulation is preferred.

The Elastomeric sheet materials with PSA, applied to tanks, vessels, duct work and air handlers for cold and chilled HVAC operations provides excellent performance. The pre-applied PSA product is particularly well suited for retrofit jobs, in operating areas, where adhesive odor and installation time are key concerns. Pre-applied pressure sensitive adhesives are limited in their installation (low temperature) and application (high temperature) service range compared to standard solvent based contact adhesives, which are more robust in both installation and application temperatures.

Elastomeric insulation with pre-applied PSA in tubular, sheet and roll forms have been successfully used in the market place because of their ease of use and faster installation time. The use of closed cell insulation as a duct liner and in air handling equipment has greatly increased in recent years as the market strives to meet more stringent air quality requirements. In most cases, additional mechanical fasteners are not required to secure the liner sheet material to the duct and equipment. SMACNA, the model building codes and NAIMA require that duct liner be installed with mechanical fasteners. The option of using mechanical fasteners in air handling units is the responsibility of the equipment manufacturer. The use of a pre-applied PSA sheet product in these applications works very well. Flexible closed cell elastomeric insulation products with pre-applied PSA are not ideal for all applications, but where they are suited, as mentioned earlier, they can provide the contractor or fabricator an advantage. As always, the surface must be clean and dry for good adhesion.

Non-Black Elastomeric Insulation

For the better part of 50 years, closed cell elastomeric insulation was black in color. The addition of carbon black to the formulation has been considered to improve the properties of Tensile strength and UV resistance to some degree. With the use of alternate non-black fillers and UV inhibitors, non-black formulations now offer the same properties as their black counter parts. In the case of this modification, the technology was ahead of the market place. The technology was in need of an application large enough to justify the commercialization of a product. Large, open ceiling food distribution centers and super stores are the current trend. The black insulation created an aesthetic problem for this type of construction. The white insulation is easier to cover with the spray-applied ceiling and wall paints used in new construction. It also makes for a neater appearing job on retrofit/repair jobs where painting may not be allowed. The new "white" elastomeric insulation products have the same physical properties and code approvals as their black counter parts.

The white elastomeric insulation product is available in most sizes and should be considered for special applications where arsthelic may be an important factor.

Non-Halogen Elastomeric Insulation

One of the first uses of flexible closed cell elastomeric materials was submarine hull and pipe insulation. Usage on ships continues to be a large market. Standard elastomeric insulation is based on a polyvinyl chloride (PVC) and Nitrile Butadiene Rubber (NBR) polymeric blend. It is also customary to use halogen-containing materials as a flame retardant. These materials have provided excellent performance to the U.S. Navy over the years. With the advent of increased highly advanced shipboard electronics today, it was determined that materials with the potential for corrosive combustion products pose a danger to the safety of the vessel. Smoke from a small fire in one compartment of the vessel could filter (via the HVAC systems) into other areas where electronic equipment is located. If the smoke contains a corrosive component, this could cause a reaction to begin that would pose a danger to the integrity of the ship at some future date. Thus, there is the need for an insulation with the same properties as the standard insulation material without halogen materials, which would cause corrosive combustion products.

The non-halogen elastomeric insulation products have very similar properties to their halogen containing counter parts but are comprised of a different polymeric base blend and alternate flame retardants. In addition to being non-halogen they are also non-black (e.g. gray or green) to easily distinguish them from the standard product. They offer the same closed cell technology that provides excellent thermal conductivity values and low permeability (water vapor intrusion). They are designed to meet the requirements of Electric Boat EB 4013, a performance based specification that the Navy is requiring for new construction on ships rather than the traditional specification Mil P 15280J used previously for this application. Electric Boat EB 4013 applies to all new construction of Navy ships (submarines and surface ships) and will eventually replace Mil P 15280J in all shipboard applications. Electric Boat EB 4013 specifies a ¼ scale cabin test to determine the combustion characteristics which is considered by the Navy to more closely duplicate real life situations than the ASTM E-84 and E-662 test procedures as specified in Mil P 15280J.

Non-military vessels such as cruise or passenger ships would be subject to other specifications outlined in the SOLAS agreement of 1974 and further defined by the IMO (International Marine Organization) and the FTP Code effective since 1998. IMO requires low flame spread, low smoke and smoke toxicity. Non-halogen materials may be used for SOLAS requirements in limited quantities and applications.

The non-halogen elastomeric insulation materials also exhibit a greater high temperature service performance rating of 250°F. This is a significant improvement over the 220°F for the standard material. This elevated temperature allows limited usage on low-pressure steam applications.

This material is also finding usage in non-ship applications because of its low corrosive properties. It contains no halogens and like the standard insulation, it is pH neutral. It widens the window for flexible elastomeric insulation in the areas of austenitic stainless steel applications such as in food processing, power plants, industrial applications and others where external stress corrosion and pitting corrosion of austenitic stainless steel is a concern.

Non-halogen elastomeric insulation materials would be installed in the same manner as standard elastomeric insulation. The same installation techniques and materials can be used. They are available in similar sizes to the standard product. The non-halogen elastomeric insulation products produced at this time are not classified as being 25/50 (flame spread/smoke development) when tested according to ASTM E-84 and as such, their use is limited to applications, which do not require such a rating. It should not be construed that these products produce less smoke, only that the smoke that is produced is less corrosive.

High Temperature Resistant Products

Demand for products with higher temperature service ratings is increasing. A considerable amount of closed cell elastomeric tubular insulation is used in the automotive industry, under the hood.

Examples of this type of application would be for insulation on automotive air conditioning lines. Temperatures under the hood are typically in the 350°F range. Products for this type of application have been on the market place for a number of years. These products are now filtering into the industrial insulation market. They are based on alternate polymers and polymer blends other than what has been the standard (PVC/NBR) for many years. With the alternate polymer base comes physical property advantages such as service temperature rating up to 350°F and improved ultra violet light (UV) resistance.

Since the product has a closed cell structure, properties such as excellent thermal conductivity and low permeability (water vapor intrusion) are maintained. The main advantages of these materials are that they remain flexible over the entire temperature range from -40°F to 350°F and not degrade at continuous high temperature exposure. Applications such are solar collectors, dual temperature and low-pressure steam lines (50 lb.) are acceptable for this material.

It can be installed using the standard installation techniques. Combustion characteristics may be different than the standard insulation products. Non 25/50 rated materials are limited to non-plenum or industrial applications. The user must verify its applicability by specified thickness before using it in commercial applications. As new polymer blends and flame retardants are developed and evaluated, new demands from the market place will be met.

ASTM Committee C-16 on Thermal Insulation, specifically subcommittee C-16.22 on Organic and Nonhomogeneous Thermal Insulation, is reviewing ASTM C 534-99 (Standard Specification for Preformed Flexible Elastomeric Cellular Thermal Insulation in Sheet and Tubular Form) for inclusion of non-halogen and high-temperature grades to complement the standard grade that has been traditionally used. The subcommittee is also in the development stage of a standard for flexible polymeric foam sheet insulation used as a thermal and sound absorbing liner for duct systems. This standard would include a grade for elastomeric closed cell materials.

Non 25/50 Rated Applications

The standard closed cell elastomeric insulation materials generally have a 25/50 (flame spread/smoke development) rating at 1-inch thickness when tested according to ASTM E-84. Most applications require only 1-inch thickness or less of elastomeric insulation to satisfy design requirements to prevent condensation, however, design parameters should be verified against the thickness recommendation. This rating is necessary to meet the requirements for many applications and building codes in the United States and Canada. Standards organizations such as the National Fire Protection Association require this rating to meet specific standards such as NFPA 90A (Standard for the Installation of Air Conditioning and Ventilating Systems) for insulation in ducts, plenums etc.

The Building Officials and Code Administration (BOCA) provides national codes for compliance to approved test of building materials (insulation) in a specific environment. Most model code organizations mandate a 75/450 rating (Interior Finishes) for all areas of the building with the exception of plenums where a 25/50 rating is required. The requirements should be reviewed with the authority having jurisdiction for the specific application.

Many architects and contractors specify that all insulation must meet the 25/50 rating because they want to have uniformity in the materials at the construction site to avoid the possibility of using the wrong material.

There are many applications that would not require the 25/50 flammability rating by code or standard. The most obvious would be outside or burial applications. In this case, other considerations may actually be more important than a 25/50 flame and smoke rating. In many military, transportation (rail car), chemical and industrial applications, the rating is not required, as is the case for many equipment applications such as air conditioners, chillers, water coolers etc. In these applications, small-scale fire tests such as UL 94, ASTM E 162, ASTM E 662 or ASTM D 3675 are the relevant test procedures.

As our insulation market grows, we should be aware of the wide range of elastomeric closed cell foams available that would provide excellent insulation qualities such as thermal conductivity and low permeability (water vapor intrusion) as a result of their closed cell structure but may not have a 25/50 (flame spread/smoke development) rating per ASTM E-84. These materials may offer other properties or benefits that would make them the preferred product for many applications.

Concluding Comments

There have been many advances in the materials classified as flexible closed cell elastomeric insulation. Physical properties such as thermal conductivity, permeability, flame and smoke rating have all been improved over the years. But in the past 5 years, the market place has seen many improvements in these materials that are designed to broaden their application scope. I have mentioned a few of these product modifications in an effort to clarify where the new products are best suited for use. As the market place becomes more competitive, I suspect there will be even more product diversification for specific applications. As these and other polymers are brought into the insulation market place, the limits of elastomeric insulation materials will be expanded.


Physical Property Test Method Units Standard Non-Halogen
Thermal C-177 BTU – in/hr .27 .27
Conductivity   – sq. ft. – °F
(k) at 75°F
Water Vapor Transmission E-96 Perm – in. .10 .05
Ozone Resistance Excellent Excellent
Operating Temperature     -70°F to 220°F -40°F to 250°F


Physical Property Test Method Units Standard High Temperature
Thermal Conductivity     .27 .30
Water Vapor .10 .05
Ozone Excellent Excellent
Operating Temperature -70°F to 220°F -40°F to 350°F