How to choose between open cell and closed cell spray foam and which is best?

What is the difference between open-cell and closed-cell spray foam?

Both open and closed cell spray foam are chemical-based insulation products that expands upon application when sprayed onto surfaces such as the sheathing between studs. The fundamental difference between open-cell and closed-cell spray foam lies in their structure:

Open-cell spray foam has a soft, sponge-like consistency with interconnected air pockets. It expands significantly when applied and remains semi-flexible after curing. Open-cell foam has a lower R-value per inch of thickness and is best suited for interior applications where soundproofing,flexibility and gap filling  are important, such as walls and ceilings. 

Closed-cell spray foam is denser, with a rigid structure formed by sealed gas pockets. It expands less than open-cell foam but creates a much more solid and waterproof insulation barrier and a higher insulation level or R-value per inch. All of these characteristics make closed cell spray foam most suitable for exterior applications and areas prone to moisture in exterior applications like walls, attics, crawl spaces, and basements. 

If you found this guide because you're thinking of having some spray foam insulation fitted, for full transparency we should probably mention that we aren't huge fans of the stuff. To put it bluntly, any spray foam insulation, both closed cell and open cell, can be problematic and we would probably only use it as a last resort. Keep on reading and we will explain more about choosing whether to use spray foam or not.    

The hidden (future) cost of spray foam insulation

One surprising fact for many North American and Canadian homeowners is that spray foam insulation can cause problems that might not be obvious at first. In countries like the UK, Europe, and Australia, many lenders have stopped offering home loans on properties that have spray foam insulation. Why? Because after a few years, spray foam can cause issues with both the building structure and the insulation itself, leading to expensive repairs of hidden damage to homes.

The real kicker is that removing spray foam insulation can cost even more than installing it in the first place. It’s a complicated and costly process to remove the foam without damaging the home. This makes it harder for homeowners to sell their properties or secure financing, as lenders know it could be an expensive problem in the future and it's their security for the money they are lending.

So, in North America, it might be wise to skip spray foam insulation altogether. By avoiding it, you can prevent a potentially costly mistake down the road, saving yourself both money and future headaches when it’s time to sell or refinance your home.     

Closed cell spray foam vs. open cell spray foam cost comparison

When it comes to spray foam insulation, both closed cell and open cell foam come with their own set of issues - and costs.

Closed Cell Spray Foam is the denser, more rigid option. It does a better job at resisting moisture and has a higher insulation value, but it’s also more expensive. Expect to pay anywhere from $1.50 to $3.00 per board foot for closed cell foam. While it might seem like you’re getting better performance, it's a hefty price for something that might end up causing more trouble in the long run.

Open Cell Spray Foam is cheaper, costing around $0.44 to $1.50 per board foot, but it’s also less durable and doesn’t handle moisture as well. It can still provide decent insulation, but it’s not going to give you the same level of protection as closed cell foam. If you’re looking to save a few bucks, this might be the way to go, but it’s far from a perfect solution.

In the end, both options are expensive for what you get, and neither is without its downsides. Whether you go with the more expensive closed cell foam or the cheaper open cell foam, you’re still dealing with a material that could create bigger problems down the road. Neither is a great option if you're trying to avoid unnecessary costs and headaches.                                               

Which is better then, open cell or closed cell spray foam?

Bear in mind that both types of spray foam insulation are petroleum-based, though they have different environmental impacts, performance characteristics and optimal uses, and the ecological impacts are significant with each. Here you can read an in-depth analysis of the health and environmental impacts of spray foam, but we will summarize briefly anyway below.

Environmental impacts of open and closed cell spray foam

Spray foam insulation has historically been criticized for its environmental impact due to the chemicals used in its production and the blowing agents that expand the foam. Open-cell spray foam generally has a lower environmental footprint because it uses water or carbon dioxide as its blowing agent, which results in fewer greenhouse gas emissions. It's not what we would call good, but it's somewhat better.

Closed-cell spray foam often relies on hydrofluoroolefin (HFO) or hydrofluorocarbon (HFC) blowing agents, some of which contribute to global warming. However, newer formulations with lower-GWP (Global Warming Potential) agents are improving its sustainability to an extent.

From a purely environmental standpoint, open-cell spray foam is the better choice due to its lower embodied carbon and reduced reliance on harmful chemicals - but, that's not the whole story.

End-of-life recyclability of spray foam (and anything it's stuck to!)

What qualifies a material as ‘green’ doesn’t end with installation - what happens to insulation when a home is renovated or demolished also matters. Open-cell spray foam is typically easier to remove, but is not widely recyclable and almost always end up in landfills.

Closed-cell spray foam is much harder to remove due to its dense and rigid nature, making it even less recyclable. Some waste-to-energy processes can repurpose it, but these are costly and rare to find. Basically anything with spray foam on it has one destination, and that’s a landfill.

Both types of spray foam have terrible end-of-life impacts, so both are losers in that respect.

Health considerations: is spray foam insulation safe?

Like many building materials, spray foam insulation has signficant potential health concerns, especially during and shortly after installation. Installers and manufacturer recommendations are that people stay out of homes for 24 to 48 hours after application. Oh really? After spraying a home with chemicals that expand and dry, the air is safe to breath a day or two later? I certainly would not be moving my family into a spray-foamed house a day after those brave installers in the hazmat suits leave.

Despite the claims that the air is safe in such a short time, people with chemical sensitivities would tell you otherwise. And they are the ones I would believe over the reassurances from companies that want my business and money.

The uses of spray foam insulation that make us cringe the most is in very air-tight homes, or worse still in shipping container homes. Just imagine for the moment filling a box with toxic chemicals and sealing yourself in there - probably not the best idea. But moving on now to the performance characteristics…

Performance comparison between open and closed cell spray foam

• Open-cell spray foam has an R-value of approximately 3.5 to 4 per inch. While this is still a good insulator, it’s not as effective as closed-cell foam at preventing heat transfer. And it is no better than typical batts, rigid foam or cellulose.
• Closed-cell spray foam boasts a higher R-value, typically 6 to 7 per inch, making it a better choice for extreme climates where maximum insulation is needed. So at least it has that going for it.

Air tightness and moisture resistance

Both types of spray foam provide reasonably good air-sealing capabilities, but there are some critical differences in how they handle moisture:

Open-cell spray foam is not a vapor barrier, meaning it allows moisture to pass through. This can be beneficial in some applications, such as attic spaces, where controlled moisture permeability helps prevent trapped condensation. But for walls it means you still a vapor barrier or vapor retarder depending on your climate.

Closed-cell spray foam acts as a vapor barrier and is highly resistant to water infiltration. This makes it a better choice for areas prone to moisture exposure, such as basements or crawl spaces.

If moisture control is a top concern, closed-cell spray foam is the better option. However, in some applications, open-cell foam’s breathability can help avoid unintended moisture buildup.

When to use open-cell vs. closed-cell spray foam insulation

Really this depends on a lot of factors, most of which are your personal priorities. If your priority is to have a sustainably built eco friendly home, or very safe can non toxic air quality, honestly that would be never. Other deciding factors are if you want :

• The most cost effective
• The highest per inch R-value
• To allow or prevent the movement of moisture
• To reduce sound transmission
• The lowest environmental impact
• The safest air quality

When to use open-cell spray foam:  

Open-cell spray foam is best suited for interior applications where moisture permeability and cost-effectiveness are priorities. It is the better of the two for walls, attics, and ceilings in mild to moderate climates where extreme insulation levels aren’t as necessary.

Since open-cell foam is vapor-permeable, it allows moisture to pass through, that can reduce the risk of trapped condensation and mold growth in areas like attic spaces. Open cell spray foam also reduces sound transmission more than closed cell due to its softer and more flexible structure.

Additionally, because it expands significantly upon application, it can effectively fill irregular cavities with less material. Homeowners looking for a more environmentally friendly option, or that which is safest for occupants, may prefer open-cell foam because of the water-based blowing agents.

When to use closed-cell spray foam:

Closed-cell spray foam is the better option for exterior walls, basements, crawl spaces, and areas prone to moisture exposure due to its high density and water resistance. As much as we don’t like this stuff, there is no disputing that for the uneven surfaces of a crawlspace floor, spray foam works very well.

It acts as a vapor barrier, preventing water infiltration and adding structural rigidity to buildings. Its higher R-value per inch compared to open cell can make it a better choice of the two for more extreme climates to reduce heating and / or cooling costs.

When applied to bare concrete basement walls it can stop the flow of moisture, so in that respect closed cell is better.

 

Our conclusions on choosing between open and closed cell spray foam

I know this is already a bit preachy, but that is because there are usually preferrable alternatives to either open or closed cell, so it is difficult to ‘recommend’ it for any application. But if we were to… for older homes with uninsulated or poorly insulated and moist basements, closed cell spray foam can be one of the more effective solutions for reducing moisture ingress from permeable concrete or CMU walls, and for insulating rim joist cavities. With newer homes that is more cheaply done with rigid foam EPS insulation.

Find the best alternative to spray foam insulation

Be sure to check out our comprehensive guide to choosing the best insulation. That and our page about choosing the best wall assembly you will likely come up with a suitable alternative to closed cell spray foam insulation or open cell foam that works well, reduces the climate impact and even saves you money. For older houses with stone walls, adding insulation can create a more comfortable living environment while also saving on heating and cooling costs. Find out the best ways to insulate stone walls for long-term comfort.