It gets cold outside in the winter but that doesn’t mean it has to be cold inside your house. Using the right kind of insulation in the right way is the key to staying warm and safe indoors. I’ve written about a variety of different types of insulation including blow in, batt insulation and mineral wool, but today I want to focus on foam insulation.

Foam insulation can come in a few different forms, the most popular of which is spray foam, but there is also foam board insulation (often called rigid foam insulation). In this post, I’ll give you a breakdown of all three types and when and where they work best. These are all fine types of foam insulation, but don’t be fooled that they all work in every situation. When poorly matched to your application, some of these can pose major problems.

Spray Foam Insulation

Open-Cell Spray Foam

  • R-Value: 3.5 per inch
  • Cost 2$ to 5$ per SF

The most affordable of the spray foam options, open-cell spray foam, is used in many applications like roof, walls, and ceilings. Open-cell foam insulation expands greatly upon installation and is fairly soft to the touch, unlike closed-cell foam. Open-cell foam is also vapor permeable which means it does not count as a vapor barrier and needs to have one applied over it. The vapor permeability of open-cell spray foam means that it can take in water and hold it, which can be a real danger. In the case of leaks, open-cell foam will absorb water and hold it against the framing and sheathing elements facilitating mold and rot.

Bottom Line: It’s a great and affordable insulation option when there is no chance of water intrusion, but you’re rolling the dice if you think it might get wet.

Closed-Cell Spray Foam

  • R-value: 6.5 per inch
  • Cost $3 to $6 per SF

Closed-cell spray foam is the king of the insulation when it comes to both R-value per inch and cost. Nothing else comes close, really. Unlike its open-cell cousin, closed-cell spray foam is not vapor permeable and will not hold water. This makes it an excellent option in case of water intrusion. It also includes binders and glues in many applications that help it to literally glue a structure together. Its strength can help prevent uplift when applied on roof decks and provide shear strength to structures. One downside is that often the blowing agents for closed-cell foam are hydrofluorocarbons, which are not so good for mother nature.

Bottom Line: It’s expensive, but wow, will this get you a structurally sound and well insulated building.

My personal preference on spray-foam insulation is that for new construction, they are an excellent option.

Spray foam is NOT reversible, which is a major problem in historic buildings, which may cause irrevocable damage to historic fabric.


It’s really for you to make up your mind as to if foam insulation is right for you, and if so, which type and where. I know, I know, lots of question and not as many answers. My hope is that armed with the information here, you can make a better decision when it does come time to insulate your house. Happy insulating and stay comfy!

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