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What Is Polyurethane Foam? The Science Behind Eco-Friendly Concrete Lifting

Published July 10, 2026

If you have gotten a quote from us in Stewartstown, York, Lancaster, Bel Air, Newark, or anywhere else in our service area, you have probably heard us say the words "polyurethane foam" more than once. Most homeowners nod along, but few actually know what the material is, what it is made of, or why we lean on it instead of the traditional mudjacking slurry that has been used since the 1930s. This post breaks down the chemistry in plain language and looks at what peer-reviewed research actually says about how the two materials compare, especially when it comes to environmental impact.

The Chemistry

What Polyurethane Foam Actually Is

Polyurethane foam used for concrete lifting is a two-component system: a polyol and an isocyanate. On their own, both are liquids. The moment our technicians combine them at the injection wand, they react chemically and begin to expand, generating carbon dioxide gas bubbles that get trapped inside the curing polymer. That is what gives the finished material its foam structure, a matrix of small, mostly closed cells rather than a solid block. Researchers who study this material for geotechnical use describe it in the same terms: a two-component foam composed of polyol and isocyanate whose geotechnical properties, strength, stiffness, and behavior under load, change depending on the density it cures to, evaluating various geotechnical properties across different foam densities in a two-component PU foam composed of polyol and isocyanate.

The density matters because it is tunable. A lower-density mix expands more and exerts more lifting force per pound of material, while a higher-density mix cures stronger and stiffer for load-bearing applications. That is part of why the same basic chemistry can lift a residential sidewalk in Willow Street and stabilize a commercial loading dock in Elkton with different formulations for each job.

Once cured, high-density polyurethane foam is chemically inert. It does not absorb groundwater, it does not dissolve, and it does not feed bacterial or fungal growth the way an organic soil-based slurry can. That inertness is also why it holds up so well underground for decades without breaking down.

The Comparison

What Mudjacking Slurry Is Made Of, By Contrast

Mudjacking, sometimes called slabjacking or pressure grouting, uses a slurry of Portland cement mixed with water, soil, and often sand. It is pumped under the slab through larger holes, where it fills voids by sheer volume and weight rather than controlled expansion. Because the mixture never fully hardens the way poured concrete does, it stays vulnerable to water infiltration for the life of the repair, and it can wash out or re-settle if the underlying soil was the original problem to begin with. That heavy, water-based slurry weighing close to 100 pounds per cubic foot is also placed on top of soil that already proved it could not support the slab, which is part of why mudjacked slabs have a well-documented tendency to sink again within a few years.

Environmental Impact

Why Foam Wins on Environmental Impact

The most-cited environmental case against mudjacking is what goes into making cement in the first place. Portland cement, the binder in every batch of mudjacking slurry, is manufactured by heating limestone in a kiln, a process that releases carbon dioxide both from the fuel burned and from the chemical breakdown of the limestone itself. A comprehensive dataset of global cement production found that process emissions from cement production reached 1.50 gigatonnes of CO2 in 2018 alone, equivalent to about 4 percent of emissions from fossil fuels, with cumulative emissions since 1928 totaling 38.3 gigatonnes. Separate peer-reviewed life-cycle work puts cement's share of global carbon emissions in the same range, generally cited at around 7 to 8 percent of global carbon emissions, roughly 70 percent of which comes from the decarbonation of limestone during clinker production. Industry-focused engineering literature reaches a similar figure, noting that Portland cement manufacturing is the third largest industrial energy consumer on a global scale and accounts for approximately 7 percent of all global industrial energy consumption, with the cement industry ranked as the second largest industrial emitter of CO2.

None of that footprint is unique to any one mudjacking job, cement is cement wherever it is poured. But it does mean that every bag of Portland cement mixed into a slurry truck carries an embedded carbon cost that a polyurethane repair simply does not, since foam jobs use a small fraction of the material volume for the same lift.

Weight is the other half of the environmental story, and it is a structural one as well. Because polyurethane foam expands to fill voids rather than being pumped in as dead weight, geotechnical researchers studying ground improvement have found it adds minimal additional load to soil that is often already struggling to support the slab above it. A recent peer-reviewed review of the technology summarized the trade-off directly: PU foam outperforms cementitious grouting in cure speed, fine-void penetrability, and faulting correction, while cement retains advantages mainly in bulk compressive strength and unit material cost. In other words, foam does the lifting job with less material, less weight, and less disturbance to the soil profile it is meant to stabilize.

The Research

What the Peer-Reviewed Studies Say

Polyurethane resin injection is not a new or untested idea in geotechnical engineering, it has a real research record behind it.

• A widely cited study published in the Canadian Geotechnical Journal examined expanding polyurethane resin as a way to remediate expansive soil foundations, establishing much of the early groundwork for how the material interacts with soil structure and moisture over time.
• A ScienceDirect study on the geotechnical characterization of expansive polyurethane resin injected into sand found the resulting composite material behaved predictably enough under testing that researchers described it as workable for controlled field application, encouraging further real-world use of closed-cell polyurethane resins in geotechnical practicefor mitigation of hazards such as liquefaction, settlement, and seismic displacement.
• A peer-reviewed review of the technology in the Journal of Current Science and Technology synthesized laboratory experiments, field case studies, and monitoring data, concluding that expanding polyurethane foam injection has emerged as a technically versatile alternative to cementitious grouting for geotechnical rehabilitation, offering rapid cure, low unit weight, and suitability for both dry and actively seeping ground conditions.
• A broader open-access review on expandable polyurethane resin injection, cataloged for soil stabilization and foundation lifting applications, describes how the physical and mechanical behavior of the cured resin depends heavily on the final density of the expanded resin, which is central to understanding its performance once injected.

Taken together, this body of research is why polyurethane injection has moved from a niche repair method to a mainstream standard for residential, commercial, and municipal concrete leveling across the country, including here in York County, Harford County, and the wider Mid-Atlantic region we serve.

Regional Relevance

Why This Matters for PA, MD, and DE Homeowners

Our service area runs from the clay-heavy soils around Lancaster and Quarryville down through the freeze-thaw cycles of York, Chester, and Delaware counties, into the sandier ground near Elkton, Newark, and the New Jersey side of the Delaware River. Every one of those soil types goes through seasonal expansion and contraction. A repair material that adds significant dead weight on top of already-stressed soil, or one that absorbs water and breaks down over a few freeze-thaw cycles, tends to fail in exactly the conditions our region sees every winter. Polyurethane foam's light weight and water resistance are not just an environmental talking point, they are why the repairs we make in Stewartstown, Fawn Grove, Bel Air, Aberdeen, Chesapeake City, and every town in between tend to outlast a traditional mudjacked slab.

Sources Cited

1. Andrew, R. M. (2019). Global CO2 emissions from cement production. Earth System Science Data, 11, 1675–1710.
2. Marceau, M., Nisbet, M., & VanGeem, M. (2007). Life Cycle Inventory of Portland Cement Concrete. Portland Cement Association; International Energy Agency Cement Sustainability Initiative (2018). Technology Roadmap: Low-Carbon Transition in the Cement Industry.
3. Buzzi, O., Fityus, S., & Sloan, S. W. (2010). Use of expanding polyurethane resin to remediate expansive soil foundations. Canadian Geotechnical Journal, 47(6), 623–634.
4. Impact of Density on Geotechnical Engineering Characteristics of High-Expansive Polyurethane Foam. International Journal of Geosynthetics and Ground Engineering (Springer Nature, 2025).
5. Geotechnical characterization of a novel material obtained by injecting a closed cell expansive polyurethane resin into a sand mass. ScienceDirect.
6. Expanding Polyurethane Foam Injection for Ground Improvement: Mechanisms of Soil-Resin Interaction, Field Verification Methods, and Practical Design Considerations. Journal of Current Science and Technology.
7. Soil Injection Technology Using an Expandable Polyurethane Resin: A Review. PMC (National Library of Medicine).

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