Spray Foam Insulation

Spray foam insulation is one of those things that many surveyors and other professionals either love or hate. And I have to admit that I was one of the haters.

But the more I consider it the more I’ve started to come round to the idea, provided they’re used in the right situations and installed correctly.

Spray Foam Insulation

Is Spray Foam insulation Eco-Friendly?

The mainstream spray foams are anything but eco-friendly as they're just a chemical cocktail. But that said all the mainstream insulations are the same.

The reason we don't think about it so much is that when we buy a sheet of pre-made insulation it’s just that, pre-made, we don’t get to see the production process as it’s done in a factory.

Spray foam on the other hand is manufactured on site, within your home, so you get to see the manufacturing process.

It is possible to get “green” or “eco” spray foams that use soy or vegetable oil. But they still mostly contain petroleum products, so while they will make your home perform in a “green” way the product itself isn’t very green at all (but as mentioned above none of the chemical based insulations are).

If you’re looking for truly green insulations you’ll need to consider things like denim insulation, sheep’s wool etc.

The main types of spray foam Insulation:

  1. Open cell foam – this type is very light (often referred to as half pound foam) and can be torn apart quite easily with your fingers. The open cells allow water vapour to pass through its structure easily.

  2. Closed cell foam – this is much denser than the open cell insulation above and is often referred to as two pound foam. It’s not easy to tear pieces off and it forms a much thicker and harder skin than the open cell foam.

    It is more expensive, but it performs much better (has a lower u-value) and is vapour resistant meaning you can apparently get away without a vapour barrier.

NB. Regardless of the claims of the manufacturers I personally would always recommend the provision of a good vapour barrier when installing any type of insulation in your home.

OPen and Closed Cell Spray Foam Insulation

Spray Foam Insulation Advantages:

  1. Airtight – provided it’s installed correctly it should provide you with an airtight seal to stop draughts coming into your home.

  2. No joints – as it’s sprayed directly onto the fabric of your home there are no gaps or joints in the insulation which would allow cold or water vapour to penetrate.

  3. Flexible use – as it’s a foam it can be installed in unusual locations such as curved spaces or unusual cavities etc.

  4. Stabilises the structure – In pure timber frame houses, as found in the US and Australia etc. the use of a closed cell spray foam can actually stabilise and strengthen the structure. It does this by physically sticking to the structure to form a single rigid infill panel.

  5. Speed of install – when installed by experienced fitters, spray foam insulation can be installed quickly.

Spray Foam Disadvantages:

  1. Cost - Closed cell spray foam is more expensive than open cell foam as the foam is much denser. This also means that it doesn’t go as far and so more chemicals are used. Foams are also more expensive than the traditional insulation materials (but they also perform better, when installed correctly).

  2. Wrong type (open cell or closed cell) – closed cell foam insulation is preferable in most climates as it has less requirement for a vapour barrier and it provides higher levels of thermal efficiency.

    Open cell foams can be used but they will need to be applied thicker as they have a lower R-value (not as thermally efficient). Open cell foams will also need a good vapour barrier fitted to the warm side of the insulation in order to prevent water vapour penetrating the insulation.

  3. Foam dries and pulls away from structure – If installed incorrectly the foam can crack or shrink and pull away from the surrounding material. If this happens the thermal efficiency will be significantly reduced and the foam should be removed and replaced.

  4. Areas missed – for obvious reasons if areas are missed the thermal efficiency will be reduced. 

  5. Difficult to remove – if something goes wrong and it has to be removed it is EXTREMELY difficult and labour intensive to remove.
DIY Spray Foam Insulation

Comparable insulation values:

The R-values (per inch) of the various insulations can be seen below (this is a rough guide as different manufacturers will have different values).

  • Phenolic Board = c. 8.3
  • Foil backed PIR (polyisocyanurate) board = c. 7.2
  • Closed cell polyurethane spray foam insulation = c. 6.8
  • Water blown closed cell spray foam = c. 5.0
  • XEPS also referred to as XPS (extruded polystyrene) = c. 4.8
  • EPS (expanded polystyrene) = c. 3.8
  • Open cell spray foam = c. 3.5
  • Loose fill cellulose = c. 3.5
  • Mineral wool = c. 3.1
  • EPS beads (expanded polystyrene) = c. 2.3

NB. For more specific R-values click here .


Be aware that the polyurethane type spray insulations are made up of hazardous chemicals that are mixed in your home. Provided they’re mixed and applied correctly by a certified installer you should have no problems.

If you do decide to go down the spray foam insulation route make sure you…

  1. Use a certified installer.

  2. Get a removal guarantee (just in case things go wrong).

  3. Don’t stay in the house while it’s being sprayed and stay out of the house for at least 24 hours while the chemicals in the foam stabilise.

Spray foam is brilliant when it comes to insulating difficult to reach areas where traditional insulation simply wouldn’t work or would be very difficult to make work. So provided you’re happy with the chemicals involved and the downsides listed above then it is a very good solution.

DIY Spray Foam Insulation

Traditional Spray Foam Alternatives:

  1. Water blown spray foam - you could consider water blown spray foam which claims to use less chemicals and therefore less risk from leaking VOC’s (volatile organic compounds).

    Although the r-values for water blown spray foams are lower than the polyurethane types due to their open cell structure.

  2. Soy based spray foam – as with water based foams they use less chemicals and are open celled so they won’t perform as well as the closed cell, much denser, polyurethane foams.

DIY Spray Foam Insulation:

There are DIY spray kits available and if you decide to get one make sure the supplier offers training on how to install it correctly and safely. Make sure you wear all the appropriate safety gear such as respirator, boiler suit, gloves etc.

If buying a DIY spray insulation kit ask what the r-value is for their product before you purchase it.

The chemicals given off during installation are dangerous so if the supplier doesn’t provide sufficient training and safety advice, go elsewhere or get a professional to install it.

Still not convinced? Check out a few of the alternatives like rigid insulation, cavity fill, denim insulation or have a look at my main insulation page.

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