The best products...
- Are mineral wool, cellular glass, cork, or wood fiber board insulation that have no blowing agents and require no flame retardants
- May be vacuum insulation with superior thermal performance
- May be halogen-free polyisocyanurate insulation with Greenguard Gold or Indoor Advantage Gold certification
But watch out for...
- Extruded polystyrene (XPS)
- Expanded polystyrene (EPS)
Products we like
Note: Manufacturers don’t pay to be listed here, and our publications are not sponsored nor supported by ads. BuildingGreen experts curate this list of products that best reflect the guidance listed above.
- Owens Corning Foamglas
- Rockwool Comfortboard
- Gutex Wood Fiberboard
- R-50 Systems Rich-E-Board
Behind the recommendations
Recommended products have at least one of the following attributes:
- recycled content
- low emissions
- avoidance of common hazardous ingredients
- superior thermal performance
- high durability
- no flame retardants
- blowing agents with little or no global warming potential
Board insulation has good thermal performance ranging from about R-4 to R-8 and is used as an integral part of a building envelope’s continuous insulation system.
Because board insulation is used on the building exterior, it is not always subject to the same material health and emissions requirements as batt insulation used inside the building envelope.
BuildingGreen bases its recommendations on a combination of performance, global warming potential, environmental impacts, and material health. For instance, mineral wool’s combined thermal performance, durability, recycled content, pest resistance, and lack of flame retardants and blowing agents make it a solid choice, even though it uses formaldehyde-based resins. Plastic foam boards, such as polyiso, XPS, and EPS, all require chemical flame retardants (and still are not as flame resistant as mineral wool).
The embodied carbon in insulation is significant. The rock or slag for mineral wool has to be melted at high temperatures, and the blowing agents used in XPS have extremely high global warming potentials (GWP). Over a lifetime of use, mineral wool has a lower overall GWP and better flame resistance than XPS, without requiring additional flame retardants. Wood insulation has low embodied carbon and is a good alternative in the right project.
Though BuildingGreen does not recommend rigid polystyrene insulation as a standalone product, energy performance is a high priority with any building, so the use of XPS or EPS may be appropriate when those are the only options available to meet functional performance goals.
- Extruded and expanded polystyrene (XPS and EPS) are petroleum based, require flame retardants, and are manufactured using a number of potentially hazardous chemicals, including benzene and styrene.
- XPS is made with high-global-warming-potential blowing agents.
- Some foam board insulations once used persistent, bioaccumulative, and toxic halogenated flame retardants. Though these compounds have been replaced with less hazardous chemistries, the long-term environmental impacts of their replacements are not fully understood.
Mineral wool board is a versatile insulation made from molten slag (a waste product of steel production) or natural rock (such as basalt or diabase), held together with a phenol-formaldehyde binder.
Mineral wool has a higher density than fiberglass, is more resistant to fire, and is better at blocking sound. It is appropriate for foundation wall and general exterior insulation.
Panels that incorporate vacuum insulation have the highest R-value of any board insulation product. Typically sandwiched between sheets of reinforced high-density polyiso, these products can have R-values of R-50 for a 1.5"-thick panel. Though it has a high first cost and has to be used where it will not be penetrated (such as roofing or behind some cladding systems), they can be the best option in applications where space is a premium or maximum R-value is required.
Cork is natural, it sequesters carbon, and it is produced through a sustainable silviculture process with a 2,000-year tradition. The material regenerates itself and can be harvested every nine years. In buildings, cork is best known as a floor-tile product and a sound-control underlayment, but it offers good thermal performance as well.
Cork insulates well, absorbs sound, and is durable in use yet ultimately biodegradable. Care has to be taken with air infiltration and insects, but cork can be an excellent choice in the right application and has been used in Europe for several decades.
Wood insulation is made from wood fiber, along with wax and small amounts of polyurethane binder. These products are often tongue-and-groove and can double as exterior sheathing, providing a more natural insulation alternative that has good thermal performance along with moisture resistance and breathability.
Of the rigid plastic foam insulations on the market, polyisocyanurate, or polyiso, may have the smallest footprint—though its impacts are still significant.
Polyiso manufacturers were among the first to move away from ozone-depleting blowing agents, and they are the first to have removed halogenated flame retardants.
Although expensive, cellular glass is naturally flame retardant, and its high compressive strength and moisture resistance make it appropriate for below-grade applications, especially sub-slab applications—where XPS currently dominates the market.
Rigid fiberglass is similar to fiberglass batts but formed into denser boardstock. It is less common as an exterior insulation. Some formaldehyde-free versions are available for use in interior applications.
Complexities of selection
Board insulation products vary widely not only in R-value but also in permeability, moisture resistance, insect resistance, fire resistance, need for flame-retardant additives, chemicals of concern, and end-use applications.