Open cell vs closed cell foam in metal building

After recognizing a need for spray polyurethane foam insulation (SPF), one of the first questions prospective customers try to tackle is “what is the difference between open cell and closed cell foam insulation?”

Spray foam insulation typically falls in one of two categories, “open cell” or “closed cell,” and each type is different in structure, where it should be applied, and performance.

Structure

Open cell spray foam is also described as a “low density” or “0.5 lb.” foam, meaning if you cut a piece of open cell foam into one cubic foot (12”x12”x12”), that piece of foam would weigh approximately half of one pound. The microscopic cells within open cell foam are just that—open— which give it a soft, fluffy feeling. We often compare the texture of open cell foam to a sponge or even angel food cake.

Closed cell spray foam, on the other hand, is also called “medium density” or “2.0 lb.” foam. Can you guess how much one cubic foot of closed cell foam weighs? The tiny cells of medium density, 2 lb. foam are closed, and the texture is very firm and rigid. After it has cured, closed cell foam is essentially a very hard plastic.

Application

Generally speaking, open cell foam is better suited for residential applications— specifically above grade in exterior walls, roof lines, attic floors, and areas that need soundproofing.

Closed cell spray foam is an incredible product below grade in your basement or crawl space because of its ability to block moisture (see below).  You’ll also see closed cell used in commercial and industrial projects, pole barns, metal buildings, and exterior applications.

Moisture Barrier

Open cell spray foam is not a moisture vapor barrier, and will allow moisture to pass. So, if you’re considering spraying foam to the roof deck of your new or existing home, you want open cell. If there’s a roof leak, water will pass through the foam, and you will quickly be able to find your problem.

At a thickness of 1.5”, many closed cell products can provide a moisture barrier to reject bulk water, and its these vapor permeability characteristics that make closed cell products perfect for insulating basement and crawl space walls. It will completely lock out the damp, musty, humid smells most basements have to fight.

R-Value

At Mullins Company, our open cell spray polyurethane foam of choice is Icynene Classic Max. Classic Max has an R-value of 3.7 per inch, and that’s pretty standard in the world of open cell products. So, if your home or building is framed on 2’x4’ studs you’ll have an R-13 in your walls.  If it’s framed on 2’x6’ studs you’ll have an R-20 in your walls.

In closed cell applications, we’ll be spraying Icynene ProSeal with an R-value of 7.0 per inch. As mentioned earlier, closed cell is commonly used in basements and crawl spaces.  We recommend a minimum of 2″ sprayed to crawl space foundation and basement walls for an R-value of 14.

Air Barrier

It’s important to keep in mind that the main benefit of all spray foam insulations is their air sealing property.  It’s not all about R-value!

At a minimum of 3.5”, most open cell foams are considered air impermeable. Because open cell foam expands at about 100x its liquid state, every crack and crevice is filled creating a very airtight environment, and that’s really what you’re after in applying spray foam.

Closed cell foam acts in a similar way, expanding roughly 40x its liquid state.  It is considered air impermeable at about 1.5” thick.

Closed-cell spray polyurethane foam (SPF) insulation offers a unique set of benefits that can help owners of metal buildings or pole barns in a number of different ways. When deciding on the type of insulation material they should use, our Colorado clients have determined the following benefits as their top reasons to use spray foam:

1. Powerful Insulator

Thousands of fasteners and welds intersecting with hundreds of beams and metal panels conduct heat into and out of a metal building, causing most other insulations to be less effective. Spray foam not only insulates the structure well but because of its expansive nature, spray foam tightly seals all the nooks and crannies that otherwise would have been left exposed, and eliminates thermal bridging concerns.

Do you want spray foam insulation in your existing metal building but don't have the time or energy to clear it out? - Consider a spray foam roof!

2. Incredible Energy Savings

Research performed at Oak Ridge National Laboratory (ORNL) in 1996 concluded that similar R-values of closed-cell spray polyurethane foam installed between metal studs in wall assemblies were 20% to 30% more energy efficient than fiberglass batts installed in similarly constructed wall assemblies. - This test did not even include factors such as air infiltration, but only heat transfer!

3. Air-tight Seal

Air sealing tops the list of the most cost effective ways to save energy. Gaps, cracks, and penetrations are where air leaks occur and are often the culprit of high energy bills and overall discomfort. Spray foam insulation fills in those crevices and voids, completely air-sealing around the through penetrations such as vents, pipes, stacks, structural supports, drains, and the like.

4. Moisture Barrier

With metal buildings, it can prove challenging and costly to identify and locate water leaks due to the irregular surfaces, angular corners and junctions. Flashings tend to move, increasing the potential for water leaks that may be hard to detect and to stop. Closed-cell spray foam conforms to the irregular surfaces, corners and junctions, forming a fully adhered, seamless waterproofing membrane that helps eliminate leaks.

Most people don't know that spray foam is also a roof which can be applied on nearly every existing roof substrate; learn more here!

5. Deters Mold

Spray foam is composed of an inert polymer that won't allow growth of mold or bacteria. This promotes better indoor air quality and a safer environment to work in.

6. Structural Strength

A topic of concern for many metal building owners is not having the ability to remove damaged wall panels after spray foam has been applied. Closed-cell spray foam has a high compressive strength. As a result, it will not only increase the structural integrity and rigidity of metal buildings, but protect the building, too. - In terms of cost, the replacement of wall panels on a metal building can cost $10 to $13 per square foot. In contrast, a closed-cell spray foam application only ranges from $3 to $5 per square foot; Less than half the cost.

7. Eco-Friendly

Spray foam is considered "green" because it reduces energy consumption, protects against mold and is designed to last a very long time, producing fewer consumed materials that would otherwise end up in the landfill.

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