Spray Foam Insulation or Fiberglass Batts?

Spray Foam Insulation photo for comparison to fiberglass batts.
Closed Cell Spray Foam Insulation is a great way to seal and insulate your home or accessory building.

Are you wondering if spray foam Insulation is the correct product for your application? Why wouldn’t you use fiberglass batts instead? We are an insulation contractor and are here to help! Each section below discusses the differences between closed-cell spray foam and fiberglass batts relative to the subject heading.

Spray Foam Insulation vs. Fiberglass Batts – Ability to Resist Heat Transfer

How does R-Value (ability to resist heat transfer) compare between spray foam and fiberglass? R-Value is one of the primary metrics used to describe the level of insulation within a home. It should be noted that R-Value is measured in a lab-based setting and assumes no air-movement. For this reason, the solution to prevent air-movement (aka vapor barrier or sealing barrier) is an important component of the overall insulation package. See the following section regarding sealing for a discussion on this.

Closed cell spray foam has an R-value of approximately R7 per inch. By comparison, Fiberglass batts have an approximate R-value of R3 to R4 per inch. Closed-cell spray foam can achieve the same insulation performance in about half the package space. This lends itself as a good solution for cathedral roofs where space is typically limited.

Ability to Seal the Building Thermal Envelope

Sealing is important when creating a building thermal envelope because it stops the movement of air across the insulating member and allows the insulation to perform it’s primary function (resisting heat transfer). Air movement around any penetration in the thermal envelope is felt as a draft and carries heat with it thereby creating a less efficient thermal envelope.

Spray foam is widely known as a premium solution for sealing a structure. Since it is sprayed as a liquid, it can penetrate gaps and cracks prior to expanding to seal them completely. Properly installed closed-cell foam achieves a vapor barrier with less than two inches of thickness and in most applications eliminates the need for a separate vapor barrier.

On the other hand, fiberglass batts typically need to be used with a separately installed vapor barrier. In many cases, a plastic sheet is installed on the ‘warm-in-winter’ side of the thermal envelope. The sheet itself is secured with staples and typically sealed around its perimeter with a caulk and any seams are taped to prevent air-leaks at those locations.

Our opinion is that spray foam provides a more durable, long-term seal. Largely because any puncture created by the fasteners holding a poly vapor barrier in place will create micro-breaks in the thermal envelope. Furthermore, any penetrations on the finished surfaces (hanging pictures on the wall, etc) will also provide opportunities for air movement.

Spray Foam Insulation vs. Fiberglass Batts – Cost Differences

As with many construction materials, costs vary with time due to many market factors. At the time of creating this document, Spray Foam is generally more expensive than fiberglass insulation with batts. There are multiple reasons for it, among some of which are as follows: Spray-foam requires more specialized equipment and skills, material prices are generally higher, and there is more prep work tied to its installation.

Reach out to us here if you are interested in assessing the differences in cost for these solutions on your project. You can submit the form here, otherwise give us a call!

Structural Implications

Did you know using closed cell spray foam in a pole building can stiffen the structure by up to ten times? As the foam is applied, it essentially glues the building members together thereby creating a monolithic structure that has significantly less deflection for a given load.

Fiberglass batts have negligible effect on structure, other than sound damping characteristics.

Sound Implications – Spray Foam Insulation vs. Fiberglass Batts


Here is a link to a helpful article about home energy, published by the MN Commerce Department. Select the pdf link near the bottom to view information about insulating your home!

There are a number of considerations for health and safety of spray foam application. This site, put together by the American Chemistry Council, Inc is a great starting place for FAQ’s and factual information regarding the application of spray foam.