The Best Materials for Eco-Friendly Insulation

I never thought I’d be the type of person to get super excited about home insulation, but here we are. Almost three decades after I listened to my father extol the virtues of cavity wall insulation, those lessons are coming home to roost.

If only my dad knew then what we know now regarding the environmental nightmare that is spray foam insulation. In the early nineties I watched that creamy goop ooze from the cracks in the brickwork of my parents’ house and thought only of how messy it looked, not about how it was contributing to global warming and potentially lowering indoor air quality in our home.

Still, many builders, renovators, and home owners looking to make their home more energy efficient, opt for XPS foam board insulation or spray foam without weighing the true cost to the environment. Indeed, with the current trend for tiny homes (which typically aren’t very eco-friendly), these dense and efficient insulation options seem like a necessity. Even some self-proclaimed eco-friendly prefabricated home builders use XPS foam boards.

In case you’re in a hurry and want to cut to the chase with my top picks for the best materials for eco-friendly insulation, here they are:

• Best stone mineral wool insulation – Roxul
• Best fiberglass insulation – Owens Corning
• Best cotton insulation (denim) – Ultra Touch

So, what’s the problem with XPS and foam insulation, and what are the eco-friendly alternatives?

XPS, EPS, and SPUF insulation – pros and cons

Extruded polystyrene (XPS) foam, expanded polystyrene (EPS) foam, and spray polyurethane foam (SPUF) are some of the most commonly used forms of insulation in residential and commercial construction. XPS boards are found primarily in floor, wall, and roof insulation. They have good compressive strength and resistance to water vapor permeability. EPS is vapor permeable, which has some advantages in some construction projects. SPUF acts as a vapor barrier and air barrier.

Despite their excellent properties for construction, these types of insulation emit massive amounts of greenhouse gases and are made with petrochemicals, making them an environmental disaster. Yes, insulating your home well will help reduce the amount of energy you need to heat and cool it, but at what overall cost to the environment?

XPS foam boards and other foam insulation products are made using blowing agents that create small bubbles of gas (these trap air to provide the insulating properties of foam). Before the 1980s, chlorofluorocarbons (CFCs) were the most common blowing agents used to make foam. As we now know, CFCs have a disastrous effect on the ozone layer protecting the planet. 

Thankfully, the production of CFCs was phased out and banned in the U.S. by 1978, with the Montreal Protocol helping to dramatically decrease their use worldwide shortly after. Although CFCs continue to be produced in other countries and smuggled around the world, their use is now just a fraction of what it once was. Unfortunately, CFCs were replaced with hydrofluorocarbons (HFCs), which don’t deplete the ozone layer, but which are around 1400 times worse than carbon dioxide as a greenhouse gas.

The U.S. Environmental Protection Agency estimates that global HFC use in construction foam accounted for a staggering 38 million metric tons of carbon dioxide equivalent in 2010. Developed countries accounted for 98% of the total. 

Recognizing the global warming potential (GWP) of the blowing agents used to make foam products, the industry has begun to investigate alternative chemicals to make foam. Two of the blowing agents with a GWP only a little higher than that of carbon dioxide include di-methyl ether and hydrofluoroolefin (HFO). Di-methyl ether is somewhat flammable, requiring special equipment to handle this safely. As for HFO, this has low to mild flammability and is rapidly becoming a favorite of many green builders because of its ease of use and relatively low GWP (6, i.e. six times that of carbon dioxide, for HFO-1234ze).

Texas-based Demilec manufacturers medium-density closed-cell spray polyurethane foam made with HFO. Other companies that offer HFO blown foam include Lapolla (Foam-Lok 2000-4G); Elastochem Specialty Chemicals (Insulthane Extreme); SES Polyurethane Systems; Covestro; Accella Polyurethane Systems; NCFI Polyurethanes; and Henry Co.

This type of HFO-blown spray polyurethane foam (SPUF) can be applied in greater thickness than other products made with HFCs. That’s because spray foams are applied on-site and rely on an exothermic chemical reaction, where heat is produced as the foam is produced. If you apply the foam too thickly all at once, heat can build up and it can catch on fire. For many spray foams, you can only apply the foam a coupe of inches thick at a time. For HFO foams, you can apply up to 6.5 inches in a single pass.

Closed cell HFO-blown SPUF has an R-value of around 6 per inch, so 8 inches will get you an R-48 rating. These R-values may not be entirely accurate, however, given that testing seems to occur shortly after applying the foam and some of the off-gassing that happens would reduce the effectiveness of the insulation. For homes where space is at a premium, but the design means heat loss is a real problem, such as a tiny home, HFO-blown SPUF is still a pretty decent option and may be more effective than XPS or EPS.

That said, don’t be taken in by manufacturers’ who claim their SPUF is soy-based and eco-friendly. The truth is that there’s very little soy in these SPUF products and the little that is present is likely genetically modified, riddled with pesticides, and responsible for deforestation anyway. SPUF is far from eco-friendly, but it is effective as insulation. 

SPUF also acts as a vapor barrier and air barrier, but because the chemicals are mixed on-site, all the off-gassing happens on-site too. With a prefabricated build, especially if this is a tiny home, there’s less time and space for these chemicals to dissipate, so your indoor air quality may be a real concern for several weeks. There’s also the fact that all of these insulation foams are based on petrochemicals, which means you’re pretty much lining your entire home with toxic flammable material.

Fortunately, it is possible to design an energy-efficient home without relying on these standard, toxic, petrochemical based foam insulation materials. One option is to consider an alternative home design that reduces your need for insulation. That might mean altering the shape of your home from long and narrow to a squarer space. Or, installing a dark polished concrete floor and south-facing thermal windows. Even then, you’re still going to need some insulation, including under that concrete slab. 

Eco-friendly insulation options

When considering alternatives to industry standard XPS boards and spray foam, you’ll need to work with your contractor to determine how well an eco-friendly insulation material will function in your specific home design. For instance, you’ll want to consider:

• How a material responds to moisture
• Whether it will meet fire safety regulations
• The potential hazards of working with the material in the factory or on-site
• How effective the material is at different thicknesses (a big factor in a narrow tiny home)
• Whether the R-value satisfies criteria for any green building qualification you’re pursuing (such as LEED)

Some of the eco-friendly materials being used today have a similar or even better performance than EPS, XPS, and SPUF. Good options for eco-friendly insulation include:

• Stone mineral wool insulation (usually referred to as Roxul, the main brand)
• Cellulose 
• Fiberglass
• Hemp
• Cotton (denim)
• Straw bales

Let’s look at each of these in turn, after a quick explanation of R-values.

Insulation and R-value

Put simply, the R-value of insulation is a measure of how well a material resists the conduction of heat. It is a measure of thermal resistance, given for a specific unit of the material barrier’s exposed area. The higher the R-value, the better the material is at preventing the conduction of heat. For a building, this means that insulation with a higher R-value can help stop heat escaping from your home. 

R-values assume steady state conditions, which means they’re not always accurate for a given material in certain situations, such as in damp, windy, weather. Knowing the qualities of an insulating material can help determine how accurate the R-value is likely to be in a particular building. 

R-values are usually additive in a linear fashion, at least for materials that are dense solid materials. This means that if a material has an R-value of 4 per inch, 3 inches would have an R-value of 12 and 6 inches would have an R-value of 24. Some materials have a stacked R-value however, meaning that the thermal resistance increases more quickly than it would if it were simply linear. Some HFO-blown foams are said to have a stacked R-value, for instance. 

Stone mineral wool (Roxul) insulation

Stone mineral wool (such as Roxul) is a recycled stone dust insulation typically comprising 75% recycled content and sometimes up to 90% recycled. Unlike foam insulation, this material actually helps slow down the spread of fire as it can withstand temperatures of up to 1800 degrees. It is also highly durable and versatile and is not affected by moisture, making it ideal for damp basements and humid climates.

Rock wool has an R-value of around 4 per inch, so to meet recommended insulation levels in California (Zone 3), you’d need some 3-4 inches of rock wool in the walls and 15 inches in the attic. For many places in Canada and the Northern United States, an energy efficient home requires wall insulation with at least an R-32 rating and closer to an R-60 rating in some places. As such, if you live in a very cold climate you may want to combine a few inches of rock wool with an HFO-blown SPUF to insulate a tiny home with little wall and loft space for insulation.

Rock wool comes in various thicknesses from 1.25 inches (R5) and is available in batts or rigid panels, just like fiberglass and XPS boards. Rock wool has a higher R-value than fiberglass, however, and is also easier and safer to install than spray foam and fiberglass. It is also one of the most eco-friendly insulation materials around and offers pretty great soundproofing to boot. Just be sure to get the right product as some rock wool is specifically designed for soundproofing while others are designed for insulation. 

One other benefit of rock wool is that termites hate it, unlike foam insulation which they’ll devour. Living in Canada, where termites are heading thanks to climate change, I’ve got my eye on rock wool as my eco-friendly insulation of choice, especially as Roxul is Energy Star rated.

Hemp insulation 

Ah, hemp. Is there nothing this material can’t do? As a renewable, natural material, hemp batting and hemp boards are an excellent option for eco-friendly home insulation. Hemp can easily be recycled and reused, takes very little energy or water input to grow and manufacture, and has an R-value of around 3.5 per inch. 

Hemp also contends fairly well with moisture, can absorb moisture from framing materials, and is naturally hypoallergenic and non-toxic, so it’s easy to handle on-site. What’s more, hemp acts as a carbon sink, helping you towards a carbon neutral home build. It may even enhance indoor air quality.

The downside is that hemp isn’t widely available and, thus, isn’t all that cheap. This would change if more people started using the material for insulation. Hemp is also resistant to compression and is hard to cut, meaning it is costly to ship and a little tricky to cut into shape to fit small space on-site. You may wish to use hemp for larger areas and rock wool (which is easy to cut with a bread knife, of all things) for fiddly areas.

Cellulose insulation 

Cellulose insulation is a non-toxic, mostly recycled (80-100%) insulation material comprising shredded newsprint. As a fan of words (can you tell?), I rather like the idea of lining my home with them. One other bonus for cellulose insulation is that it tends to be locally produced, thereby minimizing emissions associated with transporting other insulation materials. 

How can shredded newspaper be fire resistant? That’s thanks to boric acid, which is generally considered safe and non-toxic although it can cause eye and respiratory irritation. This also makes it insect resistant.

As boric acid is also an antifungal, you’d expect cellulose to be a great option for preventing the growth of yeast or mushrooms in your walls (I live in the Pacific Northwest, essentially in a rainforest, where this is a genuine concern). However, cellulose is pretty sensitive to moisture, which can affect its insulating properties, meaning it’s not the best option for damp basements or other damp environments.

For most places, though, cellulose insulation is a great option for packing walls as it allows very little air infiltration. It has an R-value of 3.66 per inch, a low environmental impact, and high performance. 

Densely packed cellulose insulation delivers a greater R-value per inch than fiberglass batting and performs more reliably than foam. And, because cellulose is often produced locally, it is significantly more eco-friendly than foam and fiberglass in terms of embodied energy.

So, if you’re building a tiny home in the desert or are confident in the seal of your building, track down some cellulose insulation. A good place to start are the Energy Star rated cellulose insulation products from Carolina Precision Fibers, a company based in North Carolina that specializes in cellulose installation, hydroseeding mulch and industrial fibers for asphalt roads.

Fiberglass insulation

Fiberglass is one of the more popular somewhat eco-friendly insulation alternatives to foam insulation. It offers an R-value of around 2.2 to 3.8 per inch, depending on its construction, and contains around 20% recycled content.

Fiberglass insulation is available mainly as batts but also as rigid boards in some places. Because it is made with glass, it has a relatively low environmental impact and offers both a good R-value and decent soundproofing (although not as good as rock wool). Compared to foam, fiberglass is much more fire resistant, being able to withstand temperatures up to 1,100 degrees Fahrenheit. Some prefabricated home companies exclusively use recycled fiberglass insulation for these reasons.

Be aware, though, that fiberglass can be a bit of a safety nightmare to install and isn’t for the fainthearted. You’ll need to wear a mask, goggles, and gloves to handle it and do your best to avoid compressing the material as this ruins performance. For tricky spots like spaces next to studs and headers, you’ll want to use a different kind of insulation as fiberglass can promote air infiltration and heat loss. Fiberglass is also sensitive to moisture, so it shouldn’t be used in basements or damp climates or against a cold concrete wall (which will have a layer of condensation). For an Energy Star rated formaldehyde-free fiberglass insulation product, check out Owens Corning.

Straw bale insulation

I grew up watching Grand Designs and dreaming of building an A-frame home with straw bale insulation. What can I say, I was an odd child with… grand designs. 

Lucky for me, straw bales turn out to be an excellent eco-friendly option. They are both a carbon sink and 100% recycled and recyclable, and have an R-value of 40! This will help you score some serious points for your LEED qualification or Net Zero build. 

Straw bale insulation used to require that you design your home so you can slot in standard sized stacked bales, which you’d then laboriously cover in mud. Fortunately, some ingenious folks (such as Modcell in the UK and Nature Built Wall Systems in Canada) have begun making prefabricated straw bale panels. This is good news because straw is quite vulnerable to damage during construction and should be kept dry at all times.

If you know of or work for a company in the U.S. making prefabricated straw bale structural integrated panel (SIPs), let me know!

Cotton insulation (denim)

The last in our list of eco-friendly insulation materials is cotton insulation (denim). This material is made almost entirely with recycled content, requiring little energy input and no toxic chemical inputs, and comes in batts. It is easy to install, non-toxic, and resistant to mold, pests, and fungus, as well as fire thanks to a non-toxic boron-based fire retardant treatment. 

Cotton batting insulation is also excellent for colder climates, especially if it’s windy (hello, Chicagoans wanting to build an eco-friendly tiny home). It has excellent soundproofing capabilities and an R-value of 3.4-3.7 per inch. 

The only real downside of cotton insulation is that it’s hard to find. Whatever you do, though, don’t be tempted to insulate your tiny home with old pairs of jeans. The effect won’t be nearly the same. Instead, you might want to check out Bonded Logic’s Energy Star Rated Ultra Touch Denim Insulation.

Summary

In summary, if you’re building an eco-friendly home and are curious about environmentally friendly insulation alternatives, there are many options out there for you to choose from. Each has its own merits for different environments and home designs. Your best bet is to talk to your contractor and/or the company designing your prefabricated home and ask them which material they would recommend. They may offer hefty discounts on some eco-friendly materials if they also use them in other projects. 

Although there is a certain economy of scale to consider, don’t feel like you have to use the same insulation materials in every area of your home. Some spaces may need more or less insulation, so you may want to choose a mixture of different materials for different areas of your home. 

One final tip for designing your home is to consider the standard sizes of the materials you’ll be using, including timber as well as straw bales, hemp boards, or whichever eco-friendly insulation you have chosen. Building to these sizes can save time, waste, and, therefore, money. If you do end up cutting batting, save the leftover insulation and use it around windows or in smaller spaces so you don’t have to rely on spray foam.