Understanding Foam Density and How It Affects Your Application
With hundreds of foam types available and countless formulations on the market, foam is one of the most versatile materials used in industrial applications today. Whether you're designing a thermal barrier, a gasket, or a filtration component, a subtle change in a foam’s chemical structure can significantly alter its physical behavior, performance, and suitability for a specific use.
What makes some foams different from others? Sometimes, it comes down to the density, specifically high vs. low density foam. Choosing the wrong density can lead to failure in the field, while selecting the right one can optimize durability, performance, and cost-efficiency. How does foam density impact performance?
How Foam Density is Determined
Foam density refers to the mass of the material per unit volume, typically expressed in pounds per cubic foot (lbs/ft³) or kilograms per cubic meter (kg/m³). It’s a measure of how much material is packed into a given space. A smaller, denser foam block can be significantly heavier than a larger one with lower density, even if they look the same to the naked eye.
Density plays a role in determining a foam’s resilience, compressibility, durability, and weight-bearing ability. Two identical-looking foam parts may perform very differently under load, based solely on their density.
During manufacturing, two main factors influence a foam’s density:
Blowing agents are chemical compounds used to create gas bubbles during the foaming process. These agents expand the resin into a cellular structure, with varying levels of expansion based on the agent's chemistry. A more expansive blowing agent results in lower density, while limited expansion yields higher density.
Chemical additives, such as stabilizers, crosslinking agents, and fillers, can further modify the foam’s characteristics. These additives influence not only the density but also properties like firmness, resistance to degradation, and processability.
Understanding these variables helps match the foam to the required application performance, including balancing weight, durability, cost, and functional behavior.
Foam Density and Its Cell Structure
The cellular structure of foam, which is the size and how the internal gas bubbles or cells are arranged, plays an equally important role in foam performance. As an example, lower density polyurethane foams tend to have larger, more open cell structures. Higher density polyurethane foams have tighter, smaller cell structures that are more compact.
That said, it’s important not to conflate density with cell type. Foam can be open-cell or closed-cell at either density level. Open-cell foams have interconnected voids that allow air, moisture, and even sound to pass through, making them ideal for applications like air or water filtration. Closed-cell foams, on the other hand, trap gas like bubbles within individual cells, creating a moisture-resistant and structurally stiffer material that’s excellent for gasketing and sealing.
Another common misconception is that density correlates with firmness. A high-density foam can be soft, and a low-density foam can be firm. Firmness is determined by the compression deflection value, which is measured independently of density. That’s why material selection should always take both variables into account when engineering a part.
Compression Deflection and Compression Set in Foam
Compression deflection (CD) refers to the amount of force, typically measured in pounds per square inch (psi), required to compress a foam material to a certain percentage of its original thickness. It gives engineers insight into how firm or soft a foam will feel and behave under load.
High compression deflection foams require more force to compress, meaning they are stiffer, firmer, and more resistant to decompression under pressure. These are ideal in applications where support, resistance to mechanical loading, or a positive seal is a priority.
Low compression deflection foams compress more easily under light loads, offering greater conformability and softness. They are typically used in applications where the seal must accommodate irregular surfaces without applying excessive pressure.
It’s important to note that compression deflection is not the same as density. A low-density foam can have a high CD if formulated with the right additives or polymer structure. Always evaluate both properties in parallel to ensure optimal performance.
Compression set (CS) measures a foam’s ability to return to its original thickness after being compressed for a prolonged period. It’s expressed as a percentage of thickness loss after compression for a specific time. A foam with a low compression set will be resilient and rebound well, while a foam with a high compression set will have a typical level of permanent deformation.
Low compression set foams maintain their original shape and sealing properties even after repeated or sustained compression. These materials are best for dynamic applications like door seals or components that undergo frequent opening and closing.
High compression set foams tend to retain some amount of deformation after load removal. While this may be acceptable in static sealing applications, it can lead to performance degradation over time in environments that require repeated cycles or reusability.
For example, a door gasket that has a high compression set that is compressed to 50% of its original thickness and experiences several open and close cycles may lose contact with the mating surface, resulting in leaks, rattling, or failure of the enclosure to remain sealed.
Density Contrast Example: Polyurethane Foam
One of the more common examples of density differences driving significant application implications is with polyurethane ester and polyurethane ether foams. Differences in density in this material drive stark differences in application use, performance, and longevity. These foams are typically categorized as either high or low density. While some of the use cases between these two classes may be used for similar uses, the application requirements often vary significantly.
When to Use High-density Polyurethane Foam
High-density polyurethane foam—typically ranging from 10 to 20 lbs./ft³—is best suited for demanding applications where strength, resilience, and long-term performance are critical. These foams often feature a microscopic open cell structure, giving them excellent resilience and low compression set under repeated use or mechanical stress.
Use cases for high-density polyurethane foam include:
Industrial gaskets and enclosures where long-term sealing under pressure low compression set is needed
Shock absorption and impact protection for heavy electronics or mechanical assemblies
Sound and vibration isolation in HVAC, automotive, or appliance applications
Gap-filling in products where consistent support and structure are required
UL 50 and UL 508 sealing applications where regulatory compliance is mandatory
Some of the most notable advantages of high-density polyurethane foams include:
Superior elongation, tensile strength, and tear resistance
Excellent compression recovery and minimal permanent deformation
High resistance to water, oils, chemicals, and ozone
Broad operating temperature range (-40°F to 194°F)
Compatibility with low-emission and low-fogging standards (e.g., SAE J-1765)
Popular brands in this category include Rogers Poron® and 3M™ Aero’s ISOLOSS™, known for their consistent performance, clean die-cutting, and compatibility with PSA lamination. These materials are often supplied in log roll format, then converted into custom rolls, sheets, or die-cut gaskets based on customer specifications.
PORON® foams are available in a range of densities, thicknesses, and compression deflection values to accommodate different performance requirements. Key features include:
Outstanding compression set resistance (ideal for maintaining seal integrity over time)
Excellent vibration and impact absorption
Low outgassing and low fogging, suitable for electronics and enclosed environments
Consistent performance over a wide operating temperature range (-40°F to 194°F)
High dielectric strength for electronic insulation applications
Compatibility with PSA lamination and precision die-cutting
UL 94 and UL50 listings
These characteristics make PORON® a go-to choice for high-end gasketing, medical device sealing, portable electronics cushioning, and automotive interior components.
ISOLOSS™ foams, part of the 3M™ Electronics Materials Solutions Division, are high-density polyurethane foams designed specifically for applications requiring advanced vibration isolation and acoustic control. Known for their energy-absorbing properties and mechanical stability, ISOLOSS™ materials excel in environments where damping, resilience, and lightweight sealing are essential.
ISOLOSS™ foams are often used in:
Aircraft interiors and structural components
Electronic enclosures where EMI shielding and noise reduction are needed
Automotive vibration damping pads and mounts
Industrial equipment where repeated impacts or oscillations occur
These foams offer similar benefits to PORON® in terms of strength and customization but are specifically engineered for acoustic isolation and dynamic mechanical energy absorption.
Find out when you should be using these types of foams here.
When to Use Lower Density Polyurethane Foam
Low-density polyurethane foam, typically, in the range of 1 to 6 lbs./ft³, is widely used for its cost-efficiency, excellent compression recovery, and suitability for air or fluid flow. These foams generally have an open-cell structure, allowing them to breathe, flex, and rebound quickly. These foam types come in both polyurethane ester and polyurethane ether formulations. Low density polyurethane ester foams have a firmer structure and are more susceptible to hydrolysis than low density polyurethane ether foams which are more flexible and resistant to deteriorating with water exposure.
Applications that benefit from low-density polyurethane foam include:
Filtration components in HVAC, automotive, and consumer electronics
Door and cabinet gaskets that require moderate sealing with consistent compression recovery
Thermal insulation pads and wraps
Vibration dampening or acoustic insulation in equipment housings
Cushioning in packaging or transport applications
Mattresses
Low-density polyurethane foams are ideal when you need flexibility, breathability, and quick rebound properties without the higher cost of dense foam materials. These foams are generally produced in buns or long boards and must be skived (sliced to thickness) before being laminated, slit, or die-cut.
The benefits of low-density foam include:
Strong resilience and bounce-back performance
Excellent thermal insulation and moderate flame resistance
Efficient sound and vibration absorption
Ability to support air and water filtration
Lower overall material costs for large-scale projects
Despite their open structure, many low-density foams can still be used for light-duty gasketing, especially when combined with PSA for secure placement and sealing.
Manufacturers like WT Burnett, Woodbridge, FXI, and others produce many types of low-density polyurethane foams, including:
Conventional Open-Cell Foams: flexible and breathable, these foams are used for light gasketing, acoustic insulation, and packaging.
Reticulated Foams: open-cell foams with uniform pore size achieved via thermal or chemical post-processing. Ideal for air and liquid filtration, these foams offer high porosity and consistent airflow.
High-Recovery Foams: engineered for superior rebound and memory after compression, these are often used in door gaskets, ventilation seals, and medical pads.
Flame-Retardant Foams: treated with additives to meet fire safety standards (such as UL 94 HF-1), common in electronics, transportation, and appliance enclosures.
Antimicrobial or Biocide-Enhanced Foams: designed for medical, cleanroom, or hygiene-critical applications, these foams help resist bacterial and fungal growth.
Custom Fabrication and PSA Tapes
At Engineered Materials Inc., we specialize in converting both high- and low-density polyurethane foams into application-ready parts that meet your exact specifications. We offer die cutting, slitting, lamination, waterjet cutting, and laser cutting, allowing us to fabricate gaskets, pads, insulators, and seals in virtually any size or shape.
Many of our foam materials can be laminated with pressure-sensitive adhesive (PSA) to simplify assembly and improve functionality. We offer a range of adhesive types, including high-tack, repositionable, and double-sided formulations, each optimized for bonding to plastics, metals, or textured surfaces.
Custom PSA-backed foam parts improve:
Ease of installation with peel-and-stick designs
Bonding strength to dissimilar substrates
Alignment accuracy during multi-step assembly
Gasket retention in dynamic or vertical applications
Whether you’re developing a high-volume automotive seal or a precision medical device component, we’ll help you select the right foam density, adhesive type, and fabrication method to meet your technical and production goals.
Contact our team today to discuss your application, request a quote, or get a sample of the foam material best suited for your needs.