I want to add wall insulation to my 1920 home. I have two locally available options -- Icynene and Tri-polymer foam. Can you advise me?


I want to add wall insulation to my 1920 home. I have two locally available options -- Icynene and Tri-polymer foam. Can you advise me?

Asked by Amy Mudd

I have a home built in 1920. I am interested in getting insulation in the walls. Two options I am looking at that are available locally are Icynene and Tri-polymer foam. I understand Icynene can be problematic as it may spill out through the woodwork and is difficult to get off our finished interior. It has been recommended we use Tri-polymer foam. Please give some feedback as I am interested in finding an environmentally friendly product with no offgassing, for a healthy home air environment.

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Alex Georgiou's picture

You're on the right track here, as the foam products you mentioned have very high R-values (between R-3.7 and R-7 per inch depending on density) and provide great performance.

  • If you are opening up the wall anyway due to a remodel, open- and closed-cell spray foams are an attractive option.
  • But in retrofit situations where you do not have an open wall -- your situation -- foam insulation is generally not at the top of the list.

Why not foam for a retrofit? The expanding properties of foam materials make it very difficult to fill the cavity completely without over-filling and damaging the building materials or structure. Spray foams also tend to offgas for a short time after installation. For a green insulation product, blown-in cellulose provides great performance and has no harmful particulates or respiratory irritants.


For your home, I would recommend using dense-pack cellulose (roughly R-3.7 per inch).

  • This is the greenest and healthiest wall insulation option, as it is made from recycled newspaper.
  • It is usually mixed with water or borate when sprayed into the wall so that it completely fills the wall cavity, which is vital to its performance.
  • Remember: insulation only performs to its rated R-value if it is in contact with all six sides of the wall cavity.


The only caveat is moisture: Cellulose does not do well when there is excess moisture in the wall cavity. It can absorb up to 130% water by weight, which degrades performance and can enable mold growth.

If moisture is an issue, I would lean more toward a formaldehyde-free fiberglass product such as Spider fiberglass insulation, offered by Johns Manville. Spider insulation only absorbs about 1% water by weight and is a formaldehyde-free product. Though fiberglass products have in the past been associated with harmful airborne particulates, the Johns Manville manufacturing process has helped make this less of an issue.

If you install fiberglass insulation of any kind, it is vital that the wall cavity is completely sealed off from the living space. That means that the connection from the drywall to the floor and ceiling must be continuous and perfect (no gaps and cracks!) and all penetrations in the wall (like electrical outlets) must be properly sealed. To assess whether this is the case, you should run a blower door test and feel for any air leaks at the penetrations and at drywall seams. In retrofit situations, your contractor will likely blow in this material; this is recommended for optimum performance as it will completely fill the wall cavity. It's best to work with a company that has done this before.

Check the installation

A good question to ask your contractor is whether they use an IR (infrared) camera to check their work. If the company does not own an infrared camera, it's a red flag because they cannot check to see if they have installed the insulation properly.

When using the infared camera, you are looking for a continuous wall temperature between the framing studs, which indicates even distribution of blown-in material. Using an infared camera is a great way check the effectiveness of any insulation product, and it is a procedure we use at Recurve to check the insulation quality at homes we audit and to insure that the insulation we install is done properly.

Long story short

Long story short: If moisture is not an issue, use blown-in cellulose.

If moisture is an issue, use Spider fiberglass insulation.

If the walls will be open, use Icynene open-cell foam (as this allows moisture to flow through it), if your budget allows -- foam products are by far the most expensive insulation options available.