Foam Board Insulation Ultimate Guide and Prices

Foam Board Insulation Ultimate Guide and Prices

The cost of foam board insulation ranges from about 30 cents per square foot to close to $1.00 depending on the type and thickness of the board. When an insulation contractor installs the insulation, the total cost of materials plus installation is $1.50 to $5.50 for most projects. This wide range of costs is explained by using boards of various thicknesses from about ½” to 2” or more.

This PickHVAC Foam Board Insulation Guide covers the types, best uses for each, their R-values, prices and more.

Foam Board Insulation 

Also called Rigid Insulation Board and Rigid Foam Insulation

Of all the types of insulation, foam board insulation is the most recent on the scene. It is lightweight, easy to install, long-lasting and can improve the energy efficiency of any home, especially those built decades ago when houses across the country were poorly insulated – or the insulation in walls and the attic has become ineffective over time due to sagging, being compressed, getting wet, etc.

Foam board insulation can be used in almost every area of the home, including foundation walls, stud walls, roofs, crawl spaces and attics. They can be found in types that work well below grade as well as above, including under slabs and radiant floors.

Biggest Pro and Con

The basic downside to rigid foam insulation is that it is more expensive than some other forms of insulation. The major advantage of foam board insulation is that it offers better insulation value for its thickness compared with batts, rolls and loose fill often found in homes.

What Is Foam Board Insulation?

This is closed cell insulation with an excellent ability to stop the flow of heat.

All types of foam board insulation are made from various kinds of plastic that are mixed with other chemicals to create rigid foam sheets or boards, similar to sheets of OSB or plywood except much less solid and made of plastic particles rather than wood.

4x8 and More in Several Thicknesses: Foam board insulation usually comes in 4x8 foot sheets, but some other sizes may be found for special applications, such as insulating garage door panels and even smaller jobs. They are commonly available in several thicknesses, ranging from ¼” to 2”, with even thicker sizes available by special order. This gives the builder or DIY homeowner a wide range of choices for each project.

Closed Cell: Foam Board Insulation is of the “closed cell” type because it is made up of foam cells that maintain their own shape. The cells are closed and have their own cell walls, and therefore are more rigid and trap a large amount of air. Most types of foam board insulation are actually about 98% air and only 2% plastic material. This means that they are very light. It also means that the trapped air inside provides for greater insulation value, known as, “R-value”.

What is R-value in insulation? Whenever we talk about insulation, we must talk about R-value. The “R” stands for Resistance. It is expressed by a number that simply tells how well an insulating material resists the transfer of heat through itself. This means that the higher the R-Value, the greater the insulating ability of the insulation.

Types of Foam Board Insulation

Did you know? Not all foam insulation boards are the same. There are several types of rigid foam insulation boards – and they have differing abilities to top the transfer of heat.

Expanded Polystyrene (EPS)

Expanded Polystyrene

EPS foam boards are made by pressing tiny beads of polystyrene into a large mold, applying heat or steam to bond them together, then cutting the large block into sheets. Though each bead is a closed cell, there are still tiny openings between the beads, meaning that moisture can pass through the board more easily than some other types of foam boards. This also means that if they get wet, they will dry as the moisture evaporates.

R-4: EPS foam boards have an R-value of approximately 4 per inch of thickness.  Because the air inside the cells does not dissipate over time, EPS foam boards do not lose their R-value as some other types do. EPS boards are usually white to distinguish them from other types of foam board insulation.

Extruded Polystyrene (XPS)

Extruded Polystyrene

XPS foam boards are made of the same base material as EPS, but instead of being made into beads it is made into foam. Then it is mixed with additives and extruded (forced) through a die, coming out as a long sheet which is then cut into appropriate lengths. This process results in the cells being more tightly packed, and moisture cannot pass through XPS boards very easily, making them a better choice where moisture is present.

R-5: XPS foam boards have an R-value of approximately 5 per inch of thickness. Until recently, it has been claimed that they do not lose their R-value over time. From recent studies, however, it appears that after about 5 years, it may be reduced to about 4.7 and will continue to be reduced even more after that. This is an issue upon which not everyone agrees.

XPS foam boards are blue, pink or green, depending on the company that manufactures them.

Graphite Polystyrene (GPS)

Graphite Polystyrene

GPS foam boards are made by infusing high-purity graphite particles into polystyrene beads. These are then molded into large blocks and cut into sheets in the same way EPS boards are. This is a fairly new product and is Considered an “advanced” foam board insulation.

R-5: With the inclusion of the graphite particles, GPS foam boards have an added ability to reflect and absorb energy that is said to improve insulation capacity by up to 30% over standard EPS. They have an R-value of almost 5 per inch of thickness, which will not change over time.

GPS foam boards can be identified by their dark silver-gray color.

Polyisocyanurate (Polyiso, or ISO)

Polyisocyanurate

Polyisocyanurate is generally used as spray foam insulation.

ISO foam boards are produced by spraying a polyurethane mixture onto either foil or paper on both sides. The result is that these insulation boards have a built-in vapor barrier, which will resist the flow of moisture better than either EPS or XPS boards, unless those boards have also had a facing material added, which isn’t common.

R-6: ISO foam boards have an R-value of approximately 6 per inch of thickness, but they lose some of their R-value in temperatures under 50 degrees F, making them a questionable choice in cold climates.

Pros and Cons of Foam Board Insulation by Type

OK, let’s compare foam board insulation types head to head by looking at their advantages and disadvantages with a reminder of their R-values.

Expanded Polystyrene (EPS) Pros and Cons

The R-4 is the lowest of any type, but that’s still better than fiberglass, mineral wool and cellulose whether in batts, rolls or loose fill insulation.

Pros:

  • Least expensive - Highest R-value per dollar
  • No loss of R-value over time
  • No CFC’s or HCFC’s used in manufacture – Considered the most “green”
  • Resists mold and mildew
  • 100% recyclable

Cons:

  • Least structural strength of all foam board insulation
  • Can attract ants and termites (if not treated)
  • Water can penetrate
  • More easily damaged than other types
  • Flammable
  • Non-Biodegradable – Once it is in a landfill, it will be there “forever”

Extruded Polystyrene (XPS) Pros and Cons 

R-5 insulation value is excellent, though you pay a little more to get it with XPS. On the upside, it offers better moisture resistance.

Pros:

  • Fairly inexpensive – slightly more than EPS
  • Higher R-value than EPS
  • More moisture and mildew resistant than EPS
  • 100% recyclable

Cons:

  • Uses HCFC’s in its manufacture – not very “green”
  • Can attract ants and termites
  • Some loss of R-value over time
  • Flammable
  • Non-Biodegradable

Graphite Polystyrene (GPS) Pros and Cons

The R-5 insulation value is very good, and this newer foam board insulation type offers a few unique advantages.

Pros:

  • Breathable and semi-permeable which helps reduce the risk of mold, rot and structural damage associated with moisture condensation
  • Manufactured with a breathable or non-breathable film
  • Maintains high R-value over time
  • Produced in 3 different styles for interior, exterior and below-grade applications, each with slightly different features
  • Same R-value as XPS, but using up to 30% less raw material

Cons:

  • The most expensive of all foam board insulation types
  • The newest type on the market; limited availability in the U.S. at this time

Polyisocyanurate (ISO) Pros and Cons

You’ll get top of the line R-6 insulation per inch of thickness with ISO.

Pros:

  • Highest R-value per inch of thickness
  • Stable over wide temperature range  -100 F to +250 F
  • Low water absorption and water vapor transmission due to foil facing
  • Resilient to many chemicals

Cons:

  • More expensive than EPS or XPS
  • Uses HCFC’s in its manufacture – not very “green”
  • Reduced insulating performance below 50 F – So using it on the interior of a basement or crawl is fine, or when the foundation is backfilled
  • More loss of R-value over time than the others

Where to Use Each Type of Foam Board Insulation

Since all types of rigid foam board insulation are not the same, there are differences as to where each type works best.

Important Note: In addition, there are certain differences that may determine which type is best in a climate that is normally warmer or colder than average. Below are some general statements about each type. If you have specific questions, a competent building supply expert or insulation contractor should be consulted.

These are the best uses. Any of them can be used in wall cavities or as attic floor insulation, though there are more cost-effective options for both. See our other Insulation Buying Guides listed below to learn more about your other insulation options.

Expanded Polystyrene (EPS)

  • Insulating concrete forms, aka ICF’s, like these https://www.youtube.com/watch?v=riXAXBYwNng are an advanced foundation system that produces high efficiency and performance
  • Can be used in roofs, walls and floors with appropriate coverings to protect against moisture, since water will penetrate it and reduce its ability to insulate
  • Commonly used for ground contact and below-grade applications such as below the slab or on the outside of foundation walls that are backfilled
  • Can be treated to resist insects
  • If used as sheathing or in addition to sheathing on the outside of a home, should be placed over house wrap

Extruded Polystyrene (XPS)

  • Often used in below-grade applications, but some studies question this practice due to retention of water over time, so we do not recommend it
  • Exterior walls – between studs or over studs with tongue & groove for better sealing, a great choice when you want a higher R-value than typical wall insulations provide
  • Attic ceilings when encapsulating an attic, though consider open cell spray foam insulation for this application too
  • Interior walls when sound-dampening is desired or there is some reason to insulate between rooms (maybe you don’t always heat a portion of your home, for example)

Graphite Polystyrene (GPS)

  • Exterior wall cavities, perimeter, roof and more – It is breathable while offering a very good R-value
  • Above slab floors, but be sure a moisture barrier is in place between the concrete and the insulation
  • Under radiant floors to keep that warm air in your living space rather than migrating down into the basement or earth

Polyisocyanurate (ISO)

  • Low slope, above-deck commercial roofing – Suitable here due to its waterproof formula
  • Can be used with hot-mopping of bitumen (tar) and won’t break down or melt
  • NOT the best choice where winter temperatures are Consistently below 50 F
  • Interior basement walls with tape on joints and spray foam on all cracks and crevices, including the sill and rim joist
  • Should not be used along with an internal vapor barrier

R-Values At a Glance

Foam Board Insulation is available in a wide variety of thicknesses. Below are some of the typical sizes found in big box stores. Some specialty sizes may only be found in building supply outlets.

Notes:

1. Not all types are available in all board thicknesses, as you can see from the chart.

2. These numbers may be changed somewhat by the addition of a facing on the product.

3. All numbers denote total R-value per thickness at the top of the column, not per board foot (listed above).

Type

1/4"

1/2"

3/4"

1"

1 1/8"

1 1/2"

2"

2 1/2"

EPS

1

1.9

3

4

--

6

8

10

XPS

--

3

4

5

--

7.5

10

12

ISO

--

3.2

4.4

6

--

--

--

--

GPS

--

--

--

--

5

7.3

--

--

Cost of Foam Board Insulation

Rigid foam insulation cost is shown in the chart.

The foam insulation board price for each is typical of what will be found in many big box stores. Prices may vary widely from one area to another and depending on supply and demand.

Prices listed are for 4’x8’ sheets (except where noted) and are rounded to the nearest $.25. The last column shows the cost per board foot, which is 1 inch thick and 1 foot square:

Type

1/2"

3/4"

1"

1 1/8"

1 1/2"

2"

2 1/2"

Board Foot $

EPS

$10

$13

$12.50

--

$17

$22

$24.50

$.24 - $.30

XPS

$15.25

$16.75

$19.50

--

$31

$35

$43

$.35 - $.40

ISO

$14

$16.75

$21.50

--

--

--

--

$.42 - $.48

GPS

--

--

--

$56 (1)

--

$31

--

$.40 - $.48

(1) This specialty 1 1/8” foam board is 4’x22’ and designed for insulating garage door panels.

Cost to Have Foam Board Insulation Installed

Insulation contractors charge $1.25 to about $2.50 to install rigid foam insulation. This equates to $1,500 to $3,000 for 1200 square feet just for installation labor.

Costs vary depending on how involved the job is; obviously, working in a crawl space is much more complicated than applying sheathing to the outside of a home. It’s always a good idea to get at least two bids on an installation job, making sure that all bidders are using the exact same product and doing the exact same job.

This doesn’t include the cost of your materials. Depending on the type you choose and the thickness of the board or boards, total cost will be $1.50 to $5.50 per square foot.

How Does Foam Board Insulation Compare to Spray Foam Insulation?

As we noted, rigid foam insulation is closed cell foam. Contractors consider both types for many jobs such as foundations, crawlspaces and attics.

Here are their relative pros and cons when comparing foam board insulation and spray foam insulation.

Closed Cell Spray Foam

Pros:

  • Provides both insulation and air sealing; all cracks and gaps are sealed as the foam expands and cures
  • High R-value; can be as much as R-7 per inch. Greater R-value is achieved by spraying the foam more thickly
  • Less time to install once preparation work is done
  • After curing, foam will stay in place without any fasteners
  • Adheres to almost any reasonably clean surface
  • Mold and mildew resistant
  • Highest R-Value of any other form of insulation

Cons:

  • Most expensive choice for insulation; up to three times the cost of other types
  • Can be messy; overspray must be prevented or removed
  • Full protective clothing and respirator must be worn during installation
  • Harmful vapors will remain in the area until the foam cures - about two hours
  • Cold temperatures can cause problems with foaming action or curing
  • R-value can degrade slightly over time

Foam Board Insulation

Pros:

  • Better choice for DIY projects than spray foam because it there is less chance for error
  • Less messy than spray foam
  • Different R-values are accomplished by using thicker boards or multiple layers
  • Foam boards are easily cut and can be installed in any temperature
  • No harmful emissions are created during installation
  • Best choice for insulating crawl spaces and basement walls
  • Some foam boards include a facing for additional R-value and vapor barrier
  • High R-Value, but less than spray foam per inch of thickness
  • Less expensive than spray foam insulation
  • Can provide additional structural strength to walls and roofs (as can closed cell or 2lb spray insulation)

Cons:

  • Since foam boards don’t expand to fill gaps, air and moisture leaks are to be expected
  • If air seal is desired, all seams between foam panels are sealed with tape and all cracks and gaps must be carefully filled with a single-component spray foam
  • More time-consuming to install than spray foam in most applications

Bottom Line

Foam Board Insulation is a great option to Consider for most of your home insulation needs. The different types, sizes, edge styles and facings available make it perhaps the most versatile of all forms of insulation. Installation requires only limited skill for the DIY homeowner, and helpers can be easily trained to help make the job go much more quickly than working alone.

Most big box stores carry a wide variety of the different products at reasonable prices, so your insulation project can be done at a minimum cost. If you do need a professional installer, many independent building contractors are familiar with foam board insulation, and you will have several to choose from and compare bids.

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