---
title: "Core Foam R-Value And Fire Safety: What The Data Shows"
description: "Core Foam R-value is 4.6 per inch at 75F mean, not 5.0. See cfiFOAM series-parallel CMU wall values and why a Class A result adds no fire-resistance rating."
url: "https://bahlfireproofing.com/core-fill-r-value-fire-safety/"
---

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# Core Foam R-Value and Fire Safety: What the Data Shows

- [Ross Bahl](https://bahlfireproofing.com/author/rossbahl/)
- September 17, 2026
- 10:00 am

Core foam r-value and fire safety: what the data shows 2

Two figures follow this masonry foam everywhere it is written about: an R-value per inch and a Class A fire result. Both are real test results, and both get quoted at conditions that do not match the question being asked. This article works through the published Core Foam R-value data and the fire data, names the test condition attached to each number, and shows which number belongs in a submittal.

Foam injected into the hollow cores of concrete block is commonly referred to as core fill insulation. Core Foam from cfiFOAM is the product our crews install for that work.

**TLDR:** Both headline numbers for this masonry foam are real test results, and both are routinely quoted at the wrong condition. Every published Core Foam R-value is a measurement taken at a stated mean temperature, and most specification errors come from repeating it at a different one. The same habit turns a surface-burning classification into a fire-resistance claim it was never able to support.

---

## The Two Numbers That Fail at Two Different Desks

Picture one drawing set. The architect fills the cores of an 8-inch block exterior wall and writes that wall into the energy compliance form using a figure lifted off a product page. The same set shows a 2-hour rated masonry corridor, and the specification calls the fill Class A, which reads in the job trailer like fire protection. Neither statement is a lie. Both are unsubstantiated.

The thermal one fails early and cheap, when a plans examiner asks how the wall R-value was calculated. The fire one fails late, because nobody argues with the words “Class A.” That claim sits in the project record until an inspector asks which listed assembly the two hours comes from, and whether that listing describes the cores as empty, grouted, or filled. Both failures are one failure: a measurement moved out of the condition it was measured under.

## What Is the Core Foam R-Value per Inch?

ICC-ES listing ESL-1648 for Core Foam Masonry Foam Insulation reports R-4.6 per inch at a 75F mean temperature, measured under ASTM C518-21, and cfiFOAM’s test data adds R-5.0 per inch at a 25F mean temperature. Federal insulation labeling under 16 CFR Part 460 and United States design R-values are stated at a 75F mean. For a commercial building in Texas, Kansas, or Oklahoma, the Core Foam R-value that belongs in a submittal is 4.6 per inch.

Mean temperature is not a footnote. In a heat flow meter apparatus the sample sits between a hot plate and a cold plate, and the mean is the average of the two. Change that average and you change the measured conductivity, so one foam legitimately produces more than one R-value.

The direction explains why the higher number exists. Heat crosses a foam cell three ways: conduction through the solid cell walls, conduction through the gas in the cell, and radiant exchange between cell walls. Gas conduction falls as the gas gets colder, radiant exchange falls off steeply as absolute temperature drops, and solid conduction barely moves. So an air-filled foam measures less conductive as the mean drops, and its R-value rises.

The foam does perform a little better on the coldest nights of the year. That benefit is real, it is small, and no compliance table is written against it. Publish 4.6 and design to nothing else.

## The Core Foam R-Value Mistake on Almost Every Masonry Package

Core Foam is a new service for us, so I will not claim a track record on it. Masonry numbers fail in one direction. Nobody gets caught overstating the chemistry. They get caught having stripped the condition off a measurement somebody else took correctly.

The pattern repeats. A value moves from a web page into a specification, from the specification into an energy model, and from the model into a stamped compliance form. At each step the qualifier falls off, because it lives in small type and the number lives in a headline. By the time a Core Foam R-value reaches a bid package, it can carry no mean temperature, no calculation method, and no block density.

What people assume goes wrong on masonry jobs is the product. What actually goes wrong is the sentence wrapped around it, and the fire version is worse, because almost nobody challenges “Class A.” Prevention is free: an R-value gets a mean temperature, a flame spread index gets a test method, and a fire-resistance rating gets a listed design.

## Why R Per Inch Times Core Depth Does Not Survive Plan Review

The shortcut is to take the foam’s R per inch, multiply it by the core depth, and call that the wall. It does not account for thermal bridging through the block webs, and that single objection disqualifies it from a code submittal.

Run the shortcut on an 8-inch unit and it lands well above anything the wall will deliver. That is not an arithmetic error. It is the wrong arithmetic, because the webs of a concrete masonry unit are solid concrete running face to face, a parallel path for heat straight around the insulation.

The recognized method is the series-parallel calculation, also called isothermal planes. CMHA TEK 06-02C lays that method out for single wythe concrete masonry walls and states that it accounts for energy loss through the webs, and cfiFOAM uses the same method for every whole-wall value in its [Thermal Properties Data Handbook for Core Foam filled block walls](https://www.cfifoam.com/wp-content/uploads/2nd-Edition-cfiFOAM-Thermal-Handbook-May-2025.pdf). A number produced any other way is useless in front of somebody who asks how a Core Foam R-value was produced.

## The Series-Parallel Core Foam R-Value Table for Filled Block Cores

Start with the two numbers that carry this article. One 8-inch concrete masonry unit with three 1-inch webs, cores filled with Core Foam, by the series-parallel method: R-8.21 in 85 pound per cubic foot lightweight block, and R-4.02 in 135 pound per cubic foot normal weight block. About a 2 times swing, identical insulation in both walls. The block the architect specified moved the wall more than the foam did.

Below is cfiFOAM’s full set for ungrouted units with three 1-inch webs, from the second edition of its Thermal Properties Data Handbook, May 2025, in calculated wall R-values with air films included. cfiFOAM publishes 8-inch and 12-inch units only.

Unit size 85 pcf 95 pcf 105 pcf 115 pcf 125 pcf 135 pcf

8 inch 8.21 7.14 6.19 5.36 4.64 4.02

12 inch 13.44 11.61 9.98 8.50 7.33 6.27

Read the columns, not just your one cell. The density penalty is consistent: moving from 85 pcf to 135 pcf costs about half the calculated value at both sizes. Thickness only pays in light block, because an 8-inch to 12-inch jump gains 5.23 points in 85 pcf block and 2.25 points in 135 pcf block. And an 8-inch lightweight unit at 85 pcf calculates to 8.21, while a 12-inch normal weight unit at 135 pcf calculates to 6.27. The thicker wall calculates lower. Density is the lever, not thickness.

## Reading the Table Honestly: Where the Core Foam R-Value Actually Lands

Two qualifiers belong with every number above, and they are the ones a bid package leaves out. The first is web geometry. That table assumes three 1-inch webs, and cfiFOAM tabulates thinner and fewer webs too. The same 8-inch unit moves a long way with them.

Here is the 8-inch set by web configuration: same foam, same method, ungrouted.

8 inch unit 85 pcf 95 pcf 105 pcf 115 pcf 125 pcf 135 pcf

3 webs, 1 inch 8.21 7.14 6.19 5.36 4.64 4.02

3 webs, 3/4 inch 9.67 8.48 7.39 6.42 5.57 4.83

2 webs, 1 inch 10.31 9.07 7.94 6.92 6.01 5.21

2 webs, 3/4 inch 11.95 10.63 9.39 8.24 7.21 6.28

Now measure the bracket. In 85 pcf block the four configurations run from 8.21 to 11.95, a spread of 3.74. In 135 pcf block they run from 4.02 to 6.28, a spread of 2.26. On a 12-inch unit the same spread runs 6.65 in light block and 4.02 in heavy block.

That is the useful finding. The supplier’s web count and web thickness are worth as much as a density step, and they rarely appear on the architectural drawings. The second qualifier is grout. Every grouted cell is concrete where foam would have been, and the same 8-inch, 85 pcf unit drops from R-8.21 ungrouted to R-6.62 with rebar cells every 96 inches and R-5.54 at 48 inches.

The working rule: read the cell for the unit actually delivered, its web configuration, and its grouting schedule, and never quote the best cell for a wall that does not match it. cfiFOAM’s handbook gives a U-factor and heat capacity for each cell, which is what COMcheck asks for. For compliance, use the calculation path in the adopted energy code, or the Standard 90.1 tables where they apply.

## Core Foam and Fire: What ASTM E84 Measured and What It Did Not

Tested to [ASTM E84 surface burning characteristics of building materials](https://store.astm.org/e0084-26a.html) and UL 723, Core Foam at a nominal 1.0 pound per cubic foot and up to 3.5 inches thick has a flame spread index of 25 or less and a smoke developed index of 450 or less, per ICC-ES listing ESL-1648. That is a surface-burning result, describing how flame travels along the face of a sample in a ten-minute tunnel test, and the listing reports it as a ceiling rather than an exact score.

Class A is a threshold, not a score. Under Section 803.1.2 of the 2021 and 2024 IBC, a Class A interior finish is a flame spread index of 0 to 25 together with a smoke developed index of 0 to 450. The listed result sits inside that band. Keep the two ideas in separate sentences, because a threshold and a measurement are different objects.

The class definitions have held steady across editions. What moved is the table assigning classes by occupancy: Section 803.11 and Table 803.11 in the 2015 IBC became Section 803.13 and Table 803.13 in the 2018, 2021, and 2024 editions. A specification still citing 803.11 was copied forward from a 2015 job. Confirm the adopted edition with the authority having jurisdiction.

Then the sentence that matters most, which is the manufacturer’s own. cfiFOAM states that its masonry foam neither adds to nor detracts from the fire-resistance rating of a CMU wall.

### A Surface Classification Is Not a Fire-Resistance Rating

Factor Surface burning classification Fire-resistance rating

Test method ASTM E84, also run as UL 723 ASTM E119, also run as UL 263

What is tested A material sample A complete assembly, as built

Duration Ten minutes Until acceptance criteria stop being met

What is measured Flame travel along a surface, plus smoke Load capacity, flame passage, heat transmission

Reported as Two dimensionless indices A time, in hours

Result names Class A, Class B, Class C 1-hour through 4-hour

Where the IBC uses it Chapter 8, interior finish Chapter 6 and Chapter 7, including Table 601

Can Core Foam add to it? The foam carries its own index No, the rating belongs to the listed assembly

Read the “reported as” row twice. One column produces an index with no units, the other produces hours, and no arithmetic converts the first into the second. That is why a Class A fill cannot add time to a wall.

We get this call regularly on rated masonry. An owner wants the cores of a corridor or demising wall filled, somebody has told them the foam is Class A, and the room assumes the wall improves in both directions at once. We ask three questions before quoting. Which listed design or code-recognized calculation is the rating coming from? Does that documentation describe the cores as empty, grouted, or filled? Who confirms that filling them keeps the assembly inside that documentation? Those are calls for the licensed architect or engineer of record and the authority having jurisdiction, and a rated-wall scope should wait until somebody can answer the second one.

The third-party evaluation that does exist is ICC-ES listing ESL-1648, reissued April 2026. It covers R-value under ASTM C518, surface burning under UL 723 and ASTM E84, and federal labeling under 16 CFR Part 460. It does not cover fire resistance, so if a submittal leans on it for hours, ask to read it. The same goes for claims about the foam’s behavior at a stated temperature that carry no test method.

## The Rest of the Published Data and What Each Number Answers

The ICC-ES listing puts nominal density at 1.0 pound per cubic foot, and cfiFOAM’s product sheet gives a finished dry density of 1.0 plus or minus 0.5, so the fill adds no meaningful dead load. The product sheet reports shrinkage under 0.5 percent, and cfiFOAM’s test data puts dimensional change at 0.5 percent or less in enclosed cavities, which separates a cured foam from a gravity-dependent fill that settles.

Moisture is the question engineers actually raise, and almost nobody answers it in context. cfiFOAM’s test data reports 10.60 perms under ASTM E96-05 and an open cell content of 40 percent by volume, so the foam is vapor permeable rather than a barrier, and cfiFOAM says it is not a waterproofing material. It also says never to inject a wet wall: no standing water in the cores and no visible wetness on the face.

cfiFOAM’s product sheet lists STC 54 to 60 in 8-inch block walls and STC 58 to 61 in 12-inch block walls, and it does not name the test standard or the block. Ask for the report before quoting either range, because sound transmission class belongs to an assembly and never to a material. The last check costs nothing: the foam should not see extended contact with surfaces above 190F, which is 88C. Boiler enclosures, kiln surrounds, flue chases, and masonry behind cooking equipment can all run past it.

## What the Energy Code Does With These Numbers in Texas, Kansas, and Oklahoma

The three states we work in do not share an energy code, and on masonry that decides which document a Core Foam R-value has to survive.

Texas is on the 2015 IECC, effective November 1, 2016 under 34 Texas Administrative Code 19.53(b), and the State Energy Conservation Office has not adopted a newer edition. None of that is ASHRAE’s doing. [ASHRAE Standard 90.1, the energy standard for buildings except low-rise residential buildings](https://www.ashrae.org/technical-resources/bookstore/standard-90-1) is a standards developer’s document. It reaches your wall only where a jurisdiction adopted it or the design elected the 90.1 path the adopted IECC permits. Where it applies, its tabulated assemblies carry the code’s own recognition.

Oklahoma’s state code body keeps the energy reference at the 2006 IECC, so an Oklahoma submittal can be judged against a 2006 edition. Kansas names the 2006 IECC as its standard for new commercial and industrial structures under K.S.A. 66-1227, but as a home-rule state adoption and enforcement sit locally, which is why the calculation method and source table belong in the submittal narrative there.

The sharpest case is not even across a state line. Dallas enforces the 2021 IECC. Fort Worth is still on the 2015. The same block wall and the same Core Foam R-value get reviewed against two editions in the same metro. The edition question is a jurisdiction question, not a state one.

One regional temptation is worth naming. A Wichita or Panhandle wall spends more hours near the cold test point than a Houston wall does, and somebody will argue the colder figure should apply there. It should not. Compliance values are stated at the standard mean temperature wherever the building sits, and the zone comes from the climate zone table in the adopted edition, never a map graphic. The 2021 IECC carried the first zone map update since 2003 and roughly ten percent of US counties changed, nearly all to warmer zones, but a jurisdiction on the 2015 IECC is judged against the 2015 map.

## How to Put These Numbers Into a Submittal Without Getting Them Sent Back

1. **State the mean temperature with every Core Foam R-value.** Write “R-4.6 per inch at 75F mean, ASTM C518-21” and the number stops being arguable.
1. **Name the calculation method and cite the source table,** publication and table number spelled out.
1. **Pull block density and unit size off the approved masonry submittal,** not off the specification’s generic call for concrete masonry units.
1. **Quote the cell for the delivered unit.** Web count, web thickness, density, and grouting all move it, so name all four.
1. **Pick the compliance path before the block ships.** Foam inside block webs is not continuous insulation, which points toward a U-factor or tabulated-assembly path.
1. **Keep the fire paperwork in two piles.** The surface-burning report covers the material, the listed design covers the hours.
1. **Check the exposure against the 190F limit** and the rest of the manufacturer’s stated limitations.
1. **Get a project-specific bid.** There is no citable published installed price for Core Foam work in this market, and any per-square-foot figure circulating as an industry number came from a lead-generation site.

## Related Reading

- [ASTM E119 versus UL 263 in fireproofing](https://bahlfireproofing.com/astm-e119-vs-vl-263-difference-fireproofing/) goes deeper into the test methods that produce hours.
- [IBC Table 601 fire-resistance rating requirements](https://bahlfireproofing.com/ib-table-601-fire-resistance-ratings/) covers where a wall’s required hours come from.
- [K-13 insulation energy performance guide](https://bahlfireproofing.com/k13-insulation-energy-performance-guide/) applies the same discipline to sprayed fiber on steel frames.
- [Rigid Foam Board vs Core Foam: The Practical Comparison](https://bahlfireproofing.com/rigid-foam-board-vs-core-foam-masonry-cavity/)

Our [Core Foam masonry insulation overview](https://bahlfireproofing.com/core-foam-masonry-insulation/) and our [Core Foam installation guide](https://bahlfireproofing.com/core-fill-installation-concrete-block-walls/) cover the product and the injection process in full.

## Frequently Asked Questions

**What is the Core Foam R-value per inch at design conditions?** R-4.6 per inch at a 75F mean temperature under ASTM C518-21, per ICC-ES listing ESL-1648. United States design R-values are stated at a 75F mean, so that is the submittal figure. The R-5.0 per inch value was measured at a 25F mean temperature.

**What is the wall R-value of an 8-inch block wall with filled cores?** By cfiFOAM’s series-parallel table for a unit with three 1-inch webs, it runs from 8.21 in 85 pcf block down to 4.02 in 135 pcf block, ungrouted. Thinner or fewer webs calculate higher, and grouted cells calculate lower.

**Does Core Foam increase the fire rating of a CMU wall?** No. cfiFOAM states that its masonry foam neither adds to nor detracts from the fire-resistance rating of a CMU wall. A wall’s rating comes from a tested and listed assembly or a code-recognized calculation.

**Is the foam a Class A material?** Its ASTM E84 result, per ICC-ES listing ESL-1648, is a flame spread index of 25 or less and a smoke developed index of 450 or less. Class A under Section 803.1.2 of the 2021 and 2024 IBC is a flame spread index of 0 to 25 with a smoke developed index of 0 to 450. That classification carries no fire-resistance time.

**Does the foam settle the way loose fill does?** cfiFOAM’s product sheet reports shrinkage under 0.5 percent, unlike a gravity-dependent fill that can settle and bridge. Voids trace to obstructed cells that stopped the injection.

**What temperature limit applies?** It should not see extended contact with surfaces above 190F, which is 88C. That rules it out of boiler enclosures, kiln surrounds, flue chases, and masonry behind cooking equipment.

## Key Takeaways

**Every Core Foam R-value carries a test condition.**

- R-4.6 per inch at a 75F mean temperature is the design figure under ASTM C518-21.
- The 5.0 figure is the 25F mean test point and never belongs in a document without that qualifier.

**Block density decides the wall, not the foam.**

- Same 8-inch unit, same fill: R-8.21 in 85 pcf block, R-4.02 in 135 pcf block.
- An 8-inch lightweight unit at R-8.21 out-calculates a 12-inch normal weight unit at R-6.27.

**Use the series-parallel table, not R per inch times core depth.**

- Multiplying R per inch by core depth ignores thermal bridging through the block webs.
- Web count, web thickness, and grouting move the wall value as much as a density step.

**A surface classification cannot become a fire-resistance rating.**

- Listed result on ASTM E84: flame spread 25 or less, smoke developed 450 or less.
- Class A per Section 803.1.2 of the 2021 and 2024 IBC is a flame spread index of 0 to 25 and a smoke developed index of 0 to 450.
- cfiFOAM states the foam neither adds to nor detracts from a masonry wall’s rating.

**The three states do not share an energy code.**

- Texas is on the 2015 IECC, Oklahoma keeps the 2006 IECC as its energy reference, Kansas names the 2006 IECC under home rule.
- Dallas enforces the 2021 IECC while Fort Worth holds the 2015, so the edition is a jurisdiction question.

If you are specifying a masonry wall and you want a crew that reads the mean temperature off the data sheet before quoting an R-value, calculates the wall by the series-parallel method instead of R per inch times core depth, keeps the surface-burning report separate from the listed assembly that carries the hours, and checks the 190F exposure before anyone drills a hole, that is the work we do throughout Texas, Oklahoma, Kansas, Nebraska, Minnesota, Wisconsin, Arizona, Missouri, and Iowa. Call me at 512-387-2111 or email ross@bahlfireproofing.com, or [Contact Bahl Fireproofing](https://bahlfireproofing.com/contact/) to get a masonry scope reviewed. Our [K-13 sprayed fiber insulation](https://bahlfireproofing.com/k13-sprayed-fiber-insulation/) page covers the steel-frame side of this work, and our [Texas service area](https://bahlfireproofing.com/texas/) page shows where we work.

---

*This article provides general educational information about masonry insulation, thermal performance, and passive fire protection, and it is not engineering, legal, or code-compliance advice. It does not replace project-specific direction from a licensed architect or engineer. Manufacturers revise their data sheets, so confirm current values and product suitability against the latest published sheet before specifying. Fire-resistance ratings depend on the tested or listed assembly and correct installation and must be confirmed against the applicable listing; a surface-burning classification is not a fire-resistance rating. Code citations reference a specific edition and the adopted edition varies by the authority having jurisdiction, so confirm requirements with your local building department and obtain a project-specific bid.*

Written for Bahl Fireproofing**Ross Bahl, Owner**

Ross owns Bahl Fireproofing, the commercial fireproofing and insulation subcontractor his family started in 1977. Every code figure on this site is checked against the published source before it goes up. [More about Ross](/ross-bahl/).

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January 27, 2026

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Most school buildings across Texas, Kansas, and Oklahoma are concrete block, and in the older ones the cores are empty. School masonry

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United States design R-values are stated at a 75F mean, so that is the submittal figure. The R-5.0 per inch value was measured at a 25F mean temperature."}},{"@type":"Question","name":"What is the wall R-value of an 8-inch block wall with filled cores?","acceptedAnswer":{"@type":"Answer","text":"By cfiFOAM's series-parallel table for a unit with three 1-inch webs, it runs from 8.21 in 85 pcf block down to 4.02 in 135 pcf block, ungrouted. Thinner or fewer webs calculate higher, and grouted cells calculate lower."}},{"@type":"Question","name":"Does Core Foam increase the fire rating of a CMU wall?","acceptedAnswer":{"@type":"Answer","text":"No. cfiFOAM states that its masonry foam neither adds to nor detracts from the fire-resistance rating of a CMU wall. A wall's rating comes from a tested and listed assembly or a code-recognized calculation."}},{"@type":"Question","name":"Is the foam a Class A material?","acceptedAnswer":{"@type":"Answer","text":"Its ASTM E84 result, per ICC-ES listing ESL-1648, is a flame spread index of 25 or less and a smoke developed index of 450 or less. Class A under Section 803.1.2 of the 2021 and 2024 IBC is a flame spread index of 0 to 25 with a smoke developed index of 0 to 450. That classification carries no fire-resistance time."}},{"@type":"Question","name":"Does the foam settle the way loose fill does?","acceptedAnswer":{"@type":"Answer","text":"cfiFOAM's product sheet reports shrinkage under 0.5 percent, unlike a gravity-dependent fill that can settle and bridge. Voids trace to obstructed cells that stopped the injection."}},{"@type":"Question","name":"What temperature limit applies?","acceptedAnswer":{"@type":"Answer","text":"It should not see extended contact with surfaces above 190F, which is 88C. That rules it out of boiler enclosures, kiln surrounds, flue chases, and masonry behind cooking equipment."}}]}]}
```