Why Open Cell Spray Foam Insulation Experts Recommend This Insulation Choice
Insulation experts recommend open cell spray foam for specific applications where its unique properties offer superior performance that other materials cannot match. They choose it primarily for two reasons: its exceptional ability to deaden sound and its effectiveness as an air barrier in places where vapor permeability is an advantage. Unlike its rigid counterpart, closed cell foam, open cell is a soft, flexible, and sponge-like material. Experts understand that this is not a one-size-fits-all product, but a specialized tool that, when used correctly, can dramatically improve a home's quietness and comfort.
A true specialist knows precisely when to leverage these strengths and, just as importantly, when to recommend a different product. This article will explain the key reasons why professionals who understand building science often choose open cell spray foam for certain parts of a home, providing insight from those who work with the material every day.
It Is an Unparalleled Sound Barrier
One of the most compelling reasons experts recommend open cell foam is for its acoustic properties. While almost all insulation provides some level of sound reduction, the structure of open cell foam makes it a standout performer in this category. Its cells are intentionally left open, creating a soft, porous texture that is extremely effective at absorbing and disrupting sound waves.
Professionals will almost always recommend open cell foam for applications where noise control is a primary goal. Common uses include:
Interior Walls: Installing it in the walls between bedrooms, bathrooms, home offices, and laundry rooms can create a much more peaceful and private home environment.
Home Theaters and Media Rooms: It helps to contain the loud sounds of movies and music while also improving the acoustic quality within the room itself.
Floors and Ceilings: It can significantly reduce the sound of footsteps and conversations between different levels of a house.
While it has a lower R-value per inch than closed cell foam, its ability to deaden sound is often far superior, making it the expert's choice for a quieter home.
It Creates an Excellent Air Seal That Can Breathe
Like all spray foams, open cell does a fantastic job of air sealing. It is applied as a liquid and expands up to 100 times its volume, filling every crack, gap, and odd-shaped cavity to create a continuous air barrier. This stops the drafts and air leaks that are a major source of energy loss and discomfort.
However, a key difference that experts value is its vapor permeability. Open cell foam allows water vapor to pass through it. This can be a significant advantage in certain climates and building assemblies. If a small amount of moisture from a minor leak were to get into a wall cavity, this permeability allows the wall to dry out to the interior. A closed cell foam application, being a vapor barrier, would trap that same moisture, potentially leading to mold and rot. For above-grade walls in a mixed or dry climate, this ability to "breathe" is a feature that building science experts appreciate.
Bonus Tip: An expert will never recommend open cell foam for below-grade applications like basements or crawl spaces. In those areas, its sponge-like nature would absorb ground moisture, leading to a complete failure of the insulation.
It Offers Long-Term Flexibility
Another reason experts recommend open cell foam is its physical properties after it cures. It remains soft and flexible for the life of the building. A house is not a static object; the wood framing can expand, contract, and shift slightly with seasonal changes in temperature and humidity.
Because open cell foam is flexible, it can move with the building structure without cracking or pulling away from the studs. This ensures that the all-important air seal remains intact over the long term. The rigid nature of closed cell foam, while excellent for adding structural strength, does not offer this same degree of flexibility to accommodate building movement over many decades.
A More Environmentally Conscious Blowing Agent
For many homeowners and contractors, the environmental impact of building materials is an important consideration. Experts often point out that open cell spray foam uses a more environmentally friendly blowing agent than many of its closed cell counterparts.
The blowing agent is the gas that is trapped in the cells of the foam and gives it its insulating properties. For open cell foam, this agent is water. During the chemical reaction, the water turns to steam, which expands the foam and then dissipates, leaving air-filled cells. Many closed cell foams, on the other hand, use chemical blowing agents that have a higher Global Warming Potential (GWP). For this reason, open cell is often the recommended choice for green building projects or for homeowners who prioritize a lower environmental footprint.
When Experts Choose Open Cell vs Closed Cell
This table shows a simplified decision-making process that an insulation expert might use when choosing between the two types of foam.
It Provides Excellent Value
Open cell spray foam is generally less expensive than closed cell foam. Because it is less dense, it requires less chemical material to fill the same space. An expert recommends it because, for the right application, it provides an outstanding level of performance for the cost. When a homeowner's primary goals are air sealing and sound control in interior or exterior walls, open cell foam can deliver those benefits at a lower price point than closed cell, making it a smart and efficient use of a project's budget.
Bonus Tip: The high expansion rate of open cell foam means it will expand beyond the studs. A professional installer will then trim the excess foam flush with the framing. A clean, smooth trim is a sign of a quality job.
Things to Consider Before Making a Decision
Before you and your contractor decide on open cell foam, it's important to be clear about your project goals.
What is the primary problem you are trying to solve? If it's noise, open cell is a great choice. If it's insulating a damp basement, it's the wrong choice.
What is the construction type? Open cell is easiest and most cost-effective to install in new construction or a major remodel where the wall cavities are open.
What are your local building code requirements for R-value? In some cases, the lower R-value of open cell might not be sufficient to meet code in a standard 2x4 wall, making closed cell the necessary choice. An expert will be able to guide you on this.
Answering Your Questions About Open Cell Foam
Can open cell foam be used in an attic?
Yes, but typically only on the attic floor of a vented attic. Here, it creates a great air seal between the living space and the attic. For the more modern approach of creating a conditioned attic, experts will almost always use closed cell foam on the underside of the roof deck for its higher R-value and moisture resistance.
What is the R-value of open cell foam?
It is typically around R-3.5 to R-4.0 per inch. In a standard 2x6 wall, this would provide an R-value of about R-19 to R-22.
Does it look different from closed cell foam?
Yes. Open cell foam has a rougher, more sponge-like appearance and is very soft to the touch. Closed cell foam is smooth, hard, and very rigid.
Can it be sprayed in an existing, finished wall?
Generally, no. The standard application requires the wall cavity to be open. There are some "injection foam" versions, but these are for specialized retrofit situations and require drilling holes in the wall.
Is it a good air barrier?
Yes, it is an excellent air barrier. This is one of its primary strengths and a key reason experts recommend it to stop drafts and reduce energy loss from air leakage.
Getting an Expert Recommendation for Your Home
Open cell spray foam is a high-performance, specialized product. Experts recommend it when its unique strengths, particularly in sound control and vapor permeability, are the perfect match for a project's needs. The key is working with a contractor who truly understands the science behind the material and can provide an honest assessment of whether it's the right choice for your home.
For homeowners in the Fresno area looking for this kind of expert guidance, the team at Supreme Spray Foam Fresno has deep experience with all types of insulation. They can help you evaluate your options and make the best decision for your project. To schedule a professional consultation, they can be reached at info@supremesprayfoamfresno.com or by calling (559) 545-0800.
Reviewer: Emma Robinson contributed her knowledge from 8 years working with the spray foam industry. Her review helped shape this content with ideas grounded in what contractors and homeowners actually value.
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