Home Basement Waterproofing Spray Foam Insulation Guide

Spray Foam Insulation Guide

Spray foam is a form of insulation that is sprayed into wall cavities or attic space. Unlike blown-in insulation, which is inserted into space in the same way, spray foam has the benefit of beginning as a liquid. As it dries, it hardens and expands, meaning you can fill a space without leaving any gaps.

The technology behind spray foam is improving all the time, and there are several different types on the market, each of which has slightly distinct properties relating to expansion, time to dry, and insulating properties.

Spray foam, therefore, is becoming an increasingly viable way to insulate your home, and sales topped $1 billion in 2015. If you’re considering making your home more insulated from sound, heat, or water, then spray foam is certainly worth considering.

This guide will walk you through the key information about spray foam so that you can make an informed decision. Be sure to also see our guide on the Average Cost of Spray Foam Insulation, which will break down the costs involved in more detail. For information on other popular insulation types, check out our fiberglass rolled and batt insulation guide and blown-in insulation guide.


Spray foam insulation essentially functions by starting as a liquid before hardening into a solid mass after drying. Despite the name, spray foam insulation isn’t exclusively sprayed. Instead, it can be injected, poured, or sprayed. In addition, foam-in-place insulation is blown into walls or other cavities, where it then hardens.


Spray foam works at different densities, which is what shapes how it hardens and sets, and therefore the best way to use it. Generally, the key question is whether you want:

  • low-density foam that expands rapidly
  • OR a slow expanding foam, which sets more slowly.

Low-Density Foam

This is sprayed into wall cavities or other confined spaces. The rapid expansion leads to the foam evenly filling the space and providing an equal layer of insulating coverage throughout.

Slow-Expanding Foam

This type doesn’t set or harden as fast. This means that it flows over obstructions before it expands or cures, thus helping it to fit around irregular shapes and more evenly fill an awkward shape. For this reason, slow-expanding foam is usually used in existing buildings that may contain wires and pipes in the wall cavities.

Another benefit of this type of foam is that the slow setting and expansion don’t place pressure on the walls – unlike low-density foams which expand indiscriminately, the slow-expanding foam will not over expand when faced with an obstacle.


To choose which one is best for your home you should, first and foremost, speak to a professional. However, you can make an estimate yourself by measuring the size of the cavity that needs to be filled, as well as checking the gaps in coverage within the cavity.

Generally, if you have a wall cavity, then it will need to be filled with slow-expanding foam. For an attic, a low-density foam may be a better option.


Perhaps unsurprisingly, spray foam requires specialist equipment, certification, and expertise to install safely and efficiently; this is not something you can do yourself over the course of a weekend.

One of the primary reasons for these requirements is spray foam needs to be protected from potential fire through the installation of an approved thermal barrier. Doing this incorrectly can present a major safety hazard for you and your home.

In addition, the building code in your state, city, or county may require additional vapor retarder to be sprayed on the foam insulation. The contractor installing the foam will know whether this is the case. If you are unsure, check with your local regulations before beginning the project.


Insulation benefits:

In general, the benefits of insulation are:

It improves your home’s energy efficiency. This means that less heat escapes from your home, and therefore your heating (and air-conditioning, in the summer) costs are reduced. This is not only beneficial for the environment but can have a major impact on your overall utility bills.

Reduces noise. In some cases, insulation also reduces sound coming through, allowing you to insulate against noisy neighbors or street sounds, or reduce sound coming from a music practice room.

Spray foam benefits:

Spray foam insulation has a number of benefits compared to other insulation types (batts, rolls, or blown-in insulation – all of which are made of fiberglass or cellulose). These benefits center on the chemical properties of the foam. Some of the benefits include:

  • Spray foam is flexible and is resistant to the wicking of moisture. This means that it will not spread moisture through your home.
  • Spray foam provides a good seal against air and is treated to be fire-resistant. This means that it can actually be a safety feature within a home.
  • Spray foam acts as a partial barrier against radon entering your home. This is because of its air barrier properties.

Spray foam, therefore, isn’t just a material to prevent heat from leaving your home – it also acts as a protective barrier, preventing potentially harmful materials from entering your home. Not only does this help your home stay warm, but it also protects things like your foundation, your appliances, and – in the case of fire – the home itself.


There are five main different types of foam, each of which has slightly different properties. Which one is best for you will be based on:

  • Your location
  • The space needing to be filled
  • And consultation with the installing contractor

Polyisocyanurate Insulation

This type of foam comes either as liquid, sprayed, or rigid foam. It is also used to make laminated insulation panels. However, the sprayed version is usually the cheapest version and also has the added benefit of molding itself around surfaces.

Polyurethane Insulation

This comes either as spray foam or rigid board. The spray version is cheaper than the pre-made board, however. This form of insulation comes in either closed-cell or open-cell (for more information on the distinction, see the section below).

Soy-based Polyurethane Insulation

These are similar to the regular polyurethane insulation, although instead of being made from petroleum or oil products, they are plant-based. This gives them eco-credentials that some consumers prefer.

However, they operate in much the same way and are compatible with all of the same equipment.

Blown-in-Blanket System (BIBS) HP

This is a relatively new development and is a combination of the BIBS single sheet method (the spray forms one single layer of the finished product) and a polyurethane spray foam.

Cementitious Insulation

As the name suggests, this form of insulation comes from cement. This brings some of the properties of cement to the final product (i.e. it is extremely rigid and tough). One version of this spray contains magnesium silicate and is designed to harden in the same way as concrete.

Less Common Foam Insulation

There are some less common types of spray foam, which include: Icynene and Tripolymer foam.

  • Icynene can be either sprayed or injected into the cavity, making it more versatile than other forms. It is also known to be a good insulator of both air and water.
  • Tripolymer foam is injected into wall cavities and specializes in fire and air insulation.


There are two main types of foam-in-place insulation – closed cell and open cell. Both of these are commonly made from polyurethane. The key differences between the two are density, insulating properties, and cost.


  • DENSITY: Closed-cell foams are more high-density as the individual cells are closed. The foam contains a gas that helps the foam expand – thus filling the space around it. Closed-cell foams tend to be denser and therefore more rigid when they set.
  • INSULATING PROPERTIES: Closed-cell insulation has a much higher R-value, providing a higher resistance to moisture and air leakage.
  • COST: However, because the material is so much denser, it is harder and more expensive to install.


  • DENSITY: Open-cell foams are less dense. They are filled with air, meaning that they are more ‘spongy’ when the set.
  • INSULATING PROPERTIES: Because of its lightness and its potentially absorbent properties, it is not possible to install open-cell foam below ground level (for example in a basement). If you were to do so, the groundwater would rapidly absorb into the foam, thus damaging the foam, the wall, and potentially even the structure of the house.
  • COST: Open-cell insulation costs a lot less.

Ultimately, spray foam insulation provides an excellent means of further insulating your home on top of things like foam rolls and batts in the attic. Spray foam, in particular, allows you to insulate wall cavities against noise and water vapor, but particularly against heat loss.

In many jurisdictions, having an energy-efficient home will allow for tax breaks – not to mention the general money saved from lower utility bills.

Although spray foam insulation can be an expensive process, you should think of it as an investment. Spending a small amount of money in the short term will not only save you money immediately but will also increase the overall value of your home, meaning you can recoup your investment many times over.

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