Is it possible for a plastic to be considered environmentally beneficial? Is mineral wool a long term
solution and consistently efficient? The following comparison of medium density spray foam and mineralwool insulations highlights the environmental strengths and weaknesses of both products.
Five categories are used to compare the products – Quality Assurance, Health and Safety, Durability, Life
Cycle Valuation and Energy Efficiency. While not an exhaustive list of the categories associated with
environmental assessments, the groupings do address the most prevalent merits/issues with each
Both mineral fibre and spray foam insulation are subject to material and installation standards. CAN/ULC-S702.1 is the material performance standard for mineral wool. CAN/ULC-S702.2 is associated with the installation of fibrous materials. CAN/ULC-S705.1 is the material standard for medium density spray foam. CAN/ULC-S705.2 is the accompanying installation standard.
Significant Differences –
- CAN/ULC S702.1 encompasses all fiber products. That is, dissimilar products, from
mineral wool to cellulose, are referenced under one standard. Conversely, spray foam
products are dedicated to specific material type – S705.1 for medium density spray foam;
S712.1 for light density spray foam.
- Both material standards for spray foam have been formalized by the spray foam industry
and sanctioned by the Canadian Standards Council. There is no corresponding
agreement in the fibre standard. While written by the fibre community, the standard has
not been ratified, nor is any of the content enforceable by an oversight organization.
- CAN/ULC-S702.2 is a generalized standard that describes the installation of various types of fibrous materials and is not referenced in the National Building Code. The CAN/ULC-S705.2 standard for spray foam is referenced in the National Building Code. As such, installers are bound by the NBC to perform daily QAP procedures.
- The material and installation standards for spray foam are certified by a third-party organization. The material standard requires that products must be certified by a testing organization that is ISO 17020 accredited. The installation standard requires that the certification process requires third-party verification of classroom testing and on-site practical confirmation. The third-party organization must be ISO 17024 certified. Conversely, the fibre industry’s standards are confirmed by the manufacturing community.
Because of the stringent training and certification required by the spray foam industry, the products are consistently installed by certified professionals. The spray foam process starts with certification, requires daily testing and subjects installations to regular third- party evaluation. Thus, the quality control process is consistently applied from manufacture of the material to in-situ installation.
Mineral wool is subject to a manufacturer-only quality assurance program. There are no
third-party plant inspections. More importantly, the product is installed by anyone –
homeowners, drywall installers, masons, carpenters. Typically, because it is difficult to
work with, and an on-site irritant, the product is installed by the most junior
Health and Safety
Both spray foam and mineral wool have been subject to significant scrutiny regarding health and safety
issues. Spray foam products use MDI isocyanate in the formation of foamed plastic insulation. During
the spraying process, the MDI is atomized, and the airborne particles are considered a “sensitizer”. Thus,
workplace asthma is associated with the installation of spray foam. To a lesser degree, some other
ingredients in the spray foam materials are considered irritants to some people.
Health concerns regarding mineral wool are well documented. And despite industry efforts to adapt
countermeasures to some of the most pertinent issues, the health and safety problems persist.
Formaldehyde binders are at the centre of health concerns. Further, “concerns regarding mineral wool
are not limited to the issue of the level of carcinogenicity. Mineral wool is known to cause skin and lung
abnormalities. Inhalation can lead to pulmonary fibrosis, a chronic disease accompanied by
breathlessness that cannot be cured”(i).
- Outgassing, or chemical release, of materials after installation of both products is a well
documented concern. The outgassing occurs relatively quickly with spray foam (within
the first ninety days). Thereafter, minute amounts of gas release occur in undetectable
amounts for approximately two years.
With mineral wool, the outgassing of formaldehyde occurs during the manufacturing
process. While two manufacturers of mineral wool insulation have announced that they
will stop using binders containing formaldehyde in “at least some of their products”, no
dates were given, and, no testing data is available to support the claims(ii).
- Appropriate Personal Protection Equipment (PPE) must be worn during the installation of both spray foam and mineral wool. When the proper PPE is worn, the dangers of both products is mitigated.
Significant Differences –
- Use of appropriate PPE is stipulated in the CAN/ULC spray foam standards. As such,
wearing the correct safety equipment is mandatory. Failure to do so can result in
decertification of the installer.
As mentioned, there is no training, certification or inspection of the mineral wool
installation. The use of PPE is recommended and voluntary.
- The CAN/ULC spray foam standards dictate that the installer must protect the entire jobsite. Mandatory barriers, warning signs and ventilation are part of the daily requirements of the installer. Failure to adequately protect the jobsite can result in loss of certification. The lack of a binding installation standard for mineral wool often means that the jobsite is inadequately protected. Airborne particulate from the mineral wool is dangerous. In fact, “there is some data which suggests mineral wool slivers in the lungs may cause cancer, by slicing DNA and causing cell mutation”(iii).
Both spray foam and mineral wool experience outgassing during and after installation of
the product. Similarly, both industries have made significant advancements regarding
the risk associated with outgassing. As a requirement of the CAN/ULC-S705.1 material
standard, every certified spray foam material must undergo a Human Health Risk
Assessment. For use in an inhabited structure, the HHRA provides guidelines as to the
adequate time before occupancy. The risk from any emissions is typically gone within
the first few hoursiv. For additional safety, the CAN/ULC-S705.2 installation standard
requires contractors to instruct residents not to return for occupation for twenty-four
hours. Further, new advancements in the spray foam materials have established zero
VOC tolerances (GreenGuard Gold Certified).
Although there is no binding material standard for mineral wool, and thus, no way to
verify the statements, manufacturers have assured the public that the use of
formaldehyde has been discontinued in selected fibre products. The majority of VOC emissions are burned off during the manufacturing process, the outgassing risk to
inhabitants of homes insulated with mineral fibre is negligible. Some mineral wool
products have also achieved GreenGuard Certification.
Spray foam, and all plastic insulations, typically grade superior than fibre products when analyzing
durability. Moisture resistance, rigidity, and adhesion to substrate equate to a product that performs
efficiently, longer. However, recent advancements to mineral wool insulation have made significant
- Spray foam and mineral wool are both resistant to moisture absorption. Each product
has hydrophobic properties, and thus, at least theoretically, resist mould growth.
Further, if water is absorbed by both products, once dried, the materials retain their
- Once cured, spray foam maintains the initial performance properties for the life of the
structure. The material will not sag or settle. Likewise, the higher density mineral wool
products are resistant to compaction and settlement.
Significant Differences –
- The advertised thermal resistance properties of spray foam remain unchanged with time.
The CAN/ULC-S705.1 material standard requires manufacturers to post the Long Term
Thermal Resistance. The LTTR value is calculated by estimating the loss of gas and is
representative of the thermal resistance after five years. Because spray foam is
manufactured ‘in-situ’, the advertised thermal resistance is the installed property.
Mineral wool advertises the thermal resistance of the material as tested in a laboratory
prior to manufacture, shipping and installation. Transportation and installation are
known to reduce the effectiveness of mineral wool.
- Environmental factors such as wind have a negative impact on all insulations. However,
the reduction in thermal resistance due to wind load is significantly less for spray foam
than that of mineral fibre. The U.S. Department of Energy studies cite air infiltration in
buildings as responsible for 40% of the energy loss in homes. Given that spray foam is
an integral air barrier material that exceeds the physical properties of most stand-alone
air barrier materials (i.e. house wrap, bitumen membranes), the effects of wind pressure
is not a detriment to thermal resistance.
- Closed-cell spray polyurethane foam is the only Class 5 flood damage-resistant insulation,
as rated by FEMA. FEMA defines a flood damage-resistant material as any building
product capable of withstanding direct and prolonged (72 hours or longer) contact with
floodwaters without sustaining significant damage. While mineral wool is water resistant,
sustained exposure to water, and subsequent saturation, renders the product unusable.
- Closed-cell spray polyurethane foam adds structural strength to roof and wall assemblies.
Factory Mutual Global measured medium density spray foam’s adhesion to concrete at
over 990psf of uplift pressure; and over 220psf of resistance to metal deck assemblies.
The National Association of Home Builders (NAHB) Research Centre concluded “during a
design racking event such as a hurricane, there would be less permanent deformation of
the wall elements and possibly less damage to a structure that was braced with SPF-filled
walls”. Further, NAHB research demonstrated that spray foam “doubled the maximum
average racking load of a plywood-clad wall assembly at 16” spacing and was 2.2 times
the racking load at 24” spacing”.(v)
Note: more recent research demonstrates that “applying a medium density spray foam fillet along wood roof member can increase the wind uplift capacity of 1⁄2” thick OSB roof sheathing panels by more than two times the uplift capacity of the control panel fastened using only nails. The results also showed
that a continuous 3” layer of medium density spray foam can increase the wind uplift capacity by as much as three times that of the control roof panel.”(vi)
The mineral wool used today is more rigid, more hydrophobic and higher in thermal
resistance than any other currently available fibre insulation. However, when compared
to plastic insulation in general, and spray foam specifically, in terms of durability, the
advantage goes to plastic insulations.
Based on research, the installation of spray foam results in significant structural benefits
and reduced building damage for impact and high winds. Spray foam performs
consistently for the life of the building. Finally, unlike other insulations, spray foam is not
negatively impacted by environmental factors like wind, cold and flooding.
Severe Weather Performance Comparison
- The raw materials used in the manufacture of spray foam and mineral wool are found in
close proximity to the products’ manufacturing facilities.
- The majority of mineral wool and spray foam manufacturers have facilities in Canada.
Thus, the distribution of the products is usually local.
- Both insulation products contribute to the reduction in the amount of energy used from fossil fuels – the most important factor in promoting sustainability.
- Spray foam has made significant changes to the blowing agent associated with outgassing. Historically, the gases used to provide spray foam with superior thermal resistance came with substantial environmental impact. The ozone depletion emissions were high and the global warming potential was similarly unacceptable. Today, with the advent of halogenated olefin blowing agents, spray foams boast zero ozone depletion, and extremely low global warming potential. Similarly, the rockwool industry has begun the process of reducing harmful emissions produced during the manufacturing process. The elimination of formaldehyde in some of the fibre products is an initial step towards lowering the pollution created during manufacture.
Significant Differences –
- The manufacturing process of spray foam products is relatively safe when compared to
that of mineral wool. Further, there is minimal embodied energy used in the extraction
of raw materials and the manufacture of materials. The spray foam ingredients are
shipped in liquid form and are contained in sealed containers throughout the
manufacturing process. There are very few pollutants emitted during the refining
process. Conversely, the mineral wool manufacturing process is the subject of significant concern.
In the summer of 2018, protests escalated in the United States in response to the
building of a mineral wool facility in Jefferson County, West Virginia. Citizens Concerned
About Rockwool said of the rockwool manufacturing facility, in a handout entitled Stop
Toxic Rockwool, “the use of both coal and slag causes the emissions to be toxic in
nature…emissions are estimated at 470 tons of volatile organic compounds and 239 tons
of nitrogen oxides a year”. Residents concerns do not seem to be unfounded: the plant
is permitted to release a total of 310,291,620 pounds of regulated air pollutants
annually.vii Additionally, in Europe, Gary Cartwright has voiced concern about the
pollution and related health risks connected to the manufacture of mineral wool: “an
elevated standard mortality ratio for lung cancer has been demonstrated in cohorts of
workers exposed to MMVF, especially in the early technological phase of mineral (rock
slag) wool production”.(viii)
- While both mineral wool and spray foam products use minimal amounts of packaging,
mineral wool packaging (plastic) is diverted directly to landfill facilities. Conversely, spray
foam is delivered to the site in metal drums (recyclable), and reusable plastic totes.
- Spray foam is delivered as raw materials and is manufactured on the jobsite. The product
comes as a liquid and is expanded up to 100 times the shipping volume. The result is less
energy used in distribution. Depending on the size of the home/structure, one spray foam
truck can hold enough material for up to five projects.
Conversely, mineral wool is shipped by volume. Thus, a minimum of one trip is required
for distribution of a project’s material requirements.
- Both products are considered useable for the life of the structure. At the end-of-cycle
deconstruction, both spray foam and mineral insulations cannot be effectively reused.
Both are disposed of at landfill sites – while spray foam will eventually degrade, the
process is essentially infinite. Save for the chemicals added during the manufacturing
process, rockwool is an organic material and will decompose naturally.
Both mineral wool and spray foam insulations are thermal insulators. Thus, both products contribute to
sustainability by reducing the amount of energy used from fossil fuels. When considering an insulation
material in terms of environmental attributes, it is often the case that the “natural” material is considered the most beneficial. Beyond the obvious thermal conductivity of a material, and not withstanding this
paper’s beforementioned product environmental impacts, in regards to a product’s energy efficiency, three characteristics must be considered – ease of installation, protection against air infiltration, and protection against moisture.
- Both mineral wool and spray foam have low thermal conductivity. The thermal
resistance of spray foam is consistently thirty percent greater than that of mineral wool.
However, per inch thermal resistance is only an attribute when space for insulation is at
a premium (i.e. retrofit applications, sloped ceilings).
Significant Differences –
- The performance of an insulation product is ultimately determined by how effectively the
material is installed. Mineral wool is quite difficult to install – the material is quite dense
and is labour intensive to cut, fit and handle. Saws are required to cut mineral wool –
the process is laborious. Mineral wool does not compress easily, and thus, squeezing the
product into odd corners and around wires is difficult. As with all batt insulation, the
extent of the care provided during installation is directly related to the effectiveness of
the finished product.
Because of the degree of difficulty installing mineral wool, it is a product often done by
apprentices and people new to construction. Thus, the installation rarely done by
tradespersons dedicated to insulation in general, and mineral wool in particular.
Spray foam installers must be CAN/ULC-S705.2 certified. As such, a spray foam installer
typically handles the product on a dedicated, daily basis. Further, because spray foam is
manufactured on site, it is ideally suited to be installed/injected into small, irregular
Gaps and voids undermine a product’s value and can render any insulation ineffective. If
any insulation is not completely tight to the inner wythe of an exterior wall, convective
loops can occur behind the insulation and reduce the product’s thermal resistance by up
to fifty percent. All board insulations, including rockwool, are susceptible to gaps caused
by irregular surfaces. Spray foam is ideally suited for irregular surfaces. The product
tenaciously bounds to the surface rather than being fitted.
The potential for gaps because of structural irregularity, and voids due to mechanical
services, are significantly reduced when using spray foam.
- Air movement through a building can increase energy use by up to forty percent,
produce interstitial moisture issues and create poor indoor air quality. Mineral wool does
not prevent the movement of air through the thermal gradient. The product requires a
separate air barrier material.
Spray foam is an integral air/vapour and thermal barrier. As such, with additional
detailing of areas not covered by spray foam (i.e. jack studs), spray foam can be a part
of an effective air barrier system.
Given that air cannot move through spray foam, neither can debris and organic material.
This makes spray foam an effective barrier to mould generation. Conversely, while
mineral wool material does not encourage mould growth by itself, the product can trap
moisture and organic material much like a fiberglass filter. This process can contribute to
- Similarly, moisture created by vapour diffusion easily passes through mineral fibre. Like
the air movement, transported moisture can also contribute to creating the conditions
necessary for organic material capture and subsequent mould growth.
Spray foam is a vapour retarder. Unlike conventional vapour retarders that provide a
single plane of resistance, spray foam is resistant to moisture movement throughout the
material. This provides consistent protection regardless of environmental conditions (i.e.
reverse vapour drive in summer conditions). Further, spray foam is not completely
impermeable to moisture movement. So, any moisture that does enter the spray foam
can also dry.
- Mineral wool and spray foam provide excellent thermal resistance. But installation
difficulties can make mineral wool unproductive at best; inadequately installed at worse.
Spray foam is installed by certified installers who have been trained and are subject to
recertification and site quality inspections.
Mineral wool requires the inclusion of separate air and vapour barriers. While all three
products can be effectively installed and contribute to the energy efficiency of the
structure, the separate processes add to the production schedule.
Spray foam is an integral thermal, air and vapour barrier material. The productivity gains
match the advantages of having a material that is resistant to all forms of energy
All insulation materials reduce pollutant and greenhouse gas emissions by reducing heating and air-
conditioning requirements of a building. This benefit almost always outweighs environmental problems associated with certain materials. All insulation materials strengthen local and regional economies by reducing expenditures on fossil fuels – generally imported from outside the region.
To be certain, insulation has the greatest potential for reducing CO2 emissions.
Mineral wool has advantages over all insulations – made from 75% recycled materials, low environmental impacts and a commitment to environmental improvement are a few. Similarly, spray foam provides licenced installers bound by a Building Code referenced standard, an integral thermal/air/vapour barrier and the advantage of manufacturing the material specific to site requirements.
Mineral wool is often considered a ‘green’ product while spray foam has traditionally struggled to be
considered an environmentally friendly product. However, labels can often be the result of
misinformation and marketing. A complete analysis of both products demonstrates that mineral wool can be a long-term solution. However, in regard to embodied energy, VOC emissions and durability, spray foam exceeds traditionally held beliefs. When the facts are examined, spray foam proves that a plastic can be green.
(viii) Gary Cartwright, “Is it time to legislate the Mineral Wool industry more tightly at EU level”, EU Today, June, 2018. The health data found within the article can be found at https://www.ncbi.nlm.nih.gov/pubmed/86666112
(i) Martin Banks, “Safety concerns over some fibre-based insulation products”, June 2018, Brussels Express.
(ii) Scott Gibson, “Mineral Wool Makers Dropping Formaldehyde Binders”, May 2017, Green Building News.
(iii) “Mineral Wool Insulation Pros and Cons”, Solar365/GreenHomes/Insulation.
(iv) Dr. Lalita Bharadwig, University of Saskatchewan, “Human Health Risk Assessment for Genyk ‘Boreal Nature”,
“Overall data suggest a low risk for adverse inhalational exposures and thus a low potential for health risk. Ambient VOC concentrations at 1 hour following the application of “Genyk PU-Foam” will be within an acceptable range for human exposure. Therefore, the recommended limiting residential occupancy time for “Genyk PU-Foam” is 1 hour and applies to residents of structures insulated with this material.”
(v) Mason Knowles, NAHB Research Centre, 1992.
vi Richard S. Duncan, “Wind Uplift Behaviour of Wood Roof Sheathing Panels Retrofitted with Spray-applied Polyurethane Foam”, University of Florida, 2007.
(vii) James Wilson, “Environmental and health concerns over mineral wool production spread from the US to Europe”, September, 2018