The Complete Guide to Foam Selection
There are hundreds of foam types and classifications. Some are specific to a particular application, while others possess qualities that make them ideal for many uses across multiple industries. The foam materials you choose for any given application impact performance and limit the fabrication techniques you can use to shape them, limiting your customization options. The foam you select can also impact your project’s budget, the cost of your product and its packaging, and other factors.
In short, choosing the right type of foam is crucial.
With so many options, where should you begin? While working with a foam fabricator like Amcon is the right first step, becoming more familiar with foam types and their uses, benefits, limitations, and specific qualities can help you make the best choice for your product or application.
Table of Contents
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Foam Qualities: What’s Important to Your Application?
Foam R-values (Insulation and Thermal Conductivity)
The R-value of a piece of foam is a numerical representation of how well the material resists heat flow. In the simplest terms, it’s how well the foam insulates. The higher the R-value, the better the piece of foam will prevent heat transfer. Closed-cell foams usually have an R-value of about 6.0 per inch—making them better insulators—while open-cell foams typically have an R-value of around 3.5 per inch. This is why foams like polystyrene are generally used for packaging and shipping temperature-controlled goods, medications, etc. Many closed-cell foams can also be used in marine or industrial foam applications to prevent heat transfer.
Porosity of Foams (Filtration, Fenestration, and Gaskets)
The porosity of a piece of foam, measured in PPI (Pores Per Inch), designates how many pores there are in a single linear inch of a piece of foam. This tells manufacturers and foam fabricators how much air and water flow will move through a piece of foam, which dictates their overall use in specific applications. Pieces of foam with a high PPI (reticulated foam) will allow greater air and water flow, making them better for filtration applications. Foams with a low PPI (neoprene) are better suited for gaskets and waterproofing. Keep in mind that the thickness of a piece of foam can also impact its ability to restrict or inhibit air and water flow.
When looking for porous foams for filtration applications, ensure they meet the High-Efficiency Particulate Air (HEPA) performance standards.
Tear Strength
Tear strength is another test of foam durability (ASTM D3574-17) that tests a piece of foam’s resistance to tearing, based on a measurement of lbs/lin inch.
Water Absorption
Similar to porosity, tests (ASTM D 3575-93 Suffix L) can also be performed to ascertain how quickly a piece of foam will absorb water.
Compression and Elongation
Compression setting and elongation are also measured using (ASTM D-3574-17) testing. Compression measures the piece of foam’s ability to hold weight, while elongation measures how long the piece of foam can be stretched before tearing.
Tensile Strength
Tensile strength is a piece of foam’s ability to resist breaking under pressure. Tests (ASTM D-3574-17) are performed on cross-sections of foam to yield specific numerical results that will tell you how durable a piece of foam is under specific PSIs.
Cushioning Curve
Cushioning curves show you how pieces of foam compress under pressure, which is particularly useful when selecting foam types and thicknesses for a specific packaging application. The cushioning curve of a piece of foam is measured based on how much it gives under different PSIs.
Flame Resistance
Tests (UL94 HF-1, FMVSS302) are performed on foam pieces to test their flammability and ensure they pass safety standards.
Sound Dampening and Absorption
Foam plays a prominent role in reducing noise and vibrations in many settings, and both open and closed cell foams can be used to control the acoustics of a room. Half-inch foam layers can absorb sound frequencies between 1200 and 7000 Hz. Manufacturers can also use thicker foam combined with dense vinyl to absorb sound frequencies as low as 500 Hz.
Force Deflection
Force deflection measures the firmness and flexibility of a piece of foam. It essentially tells you how “soft” the foam is, which can be useful for cushioning applications.
Choosing the Right Foam Type: Open Cell vs. Closed Cell Foam
Many of the foam you will encounter for any application can be broken down into one of two categories:
- Open-cell foam
- Closed-cell foam
The primary difference between these two types of foam is at the molecular level. Specifically, the foam’s permeability—how well liquids and gasses can flow through the material. The permeability of a piece of foam can change how dense it is, how well it protects and insulates, and whether it makes a good foam filter or foam gasket. These fundamental differences make open and closed cell foams ideal for very different uses. If you are confronted with these terms during foam selection, be prepared to know the primary differences between them.
The Basics of Open Cell Foam
Open-cell foam is a light and soft type of foam that is regularly used to protect small, sensitive objects and for cushioning applications. Most people know this type of foam as the “memory foam” used in foam mattresses and other types of residential and commercial furniture.
The most defining features of open-cell foam are its viscoelasticity and low density. Viscoelasticity combines two major components: viscosity and elasticity. Viscosity is a material’s resistance to deformation due to compression. When an inward force is applied to open-cell foam, it compresses. When the force is removed, the foam returns to its natural shape. Elasticity refers to a material’s ability to resist deformation when it is stretched rather than compressed. When combined, viscosity and elasticity allow for a viscoelastic material like open-cell foam to be compressed and stretched to specific lengths while still being able to maintain its original shape.
At a molecular level, the cells of open-cell foam are deliberately left open, making the foam less dense, softer, and more flexible. It also allows air and liquid to pass through the material, which is why open-cell foam is commonly used in filtration and acoustic applications. Many open cell foams have a density of about .5 pounds per cubic foot.
Common applications for open-cell foam include:
- Packaging for small and sensitive products (circuit boards, CPUs, microprocessors, and medical devices)
- Cushioning (mattresses, seating, pillows, and bed wedges)
- Orthotics
- Athletics (wall pads, pit foam blocks, landing mats)
- Fenestration
- Filtration
Common types of open-cell foam include:
- Ether-based polyurethane
- Ester-based polyurethane
- Reticulated foam
The Basics of Closed Cell Foam
Closed-cell foam is a structurally rigid, more dense type of foam than its open cell counterpart. This makes it more ideal for heavier packaging applications, sound and thermal insulation, waterproofing, etc.
At the molecular level, the cells of closed-cell foam materials are encapsulated or closed off from one another. The cells are also more tightly bunched together, creating a denser and more rigid (but generally lightweight) structure to the material. These properties create a non-breathable material with the capability to prohibit the flow of water and air. Many closed-cell foams have a density of about 1.75 pounds per cubic foot or more.
Because closed-cell foams do not have viscoelastic properties similar to open-cell foams, they often provide greater support, meaning heavier products can be better protected for packaging applications. Closed-cell foams also have a greater ability to absorb shocks. While open-cell foam may be more comfortable to lie down on (making them suitable for comfort cushioning), closed-cell foams are ideal for protective cushioning applications like athletic or protective padding and mats.
Common applications for closed-cell foams include:
- Packaging of heavier, more dense items
- Insulation
- Sound dampening
- Gaskets and seals
- Marine applications
- Waterproofing
- Outdoor seating
Common types of closed-cell foam include:
- Polyethylene Foam
- Beaded Polyethylene Foam
- Crosslinked Polyethylene Foam
- Expanded Polystyrene Foam
- Neoprene
Choosing the Right Foam Type: Expanded Polyethylene Foam vs. Expanded Polypropylene Foam
What is Expanded Polyethylene Foam?
Expanded polyethylene foam (EPE) is a thermoplastic resin that can be melted and cooled to create a various shapes. Because it is flexible and has an excellent strength-to-weight ratio, the closed-cell foam is a favorite for those working with packaging applications. It’s also resistant to water, oils, and many other chemicals, insulates well, and can be made available in varying densities.
The chemical makeup of EPE is similar to most plastics, which allows it to be subjected to high temperatures without losing its chemical structure. The material can also be recycled and reshaped multiple times, reducing its impact on the environment.
Expanded polyethylene foam is a fantastic choice for a variety of applications, particularly in packaging. It offers strong shock absorbency, chemical and static resistance, insulation, and can be used in a wide temperature range. It can also be dyed multiple colors, allowing it to be colored coded for use.
Other uses for EPE foam include:
- Marine floatation applications and life preservers
- Insulation
- Water-proofing and joint fillers
- Athletic mats and protective athletic padding
What is Expanded Polypropylene Foam?
Expanded polypropylene foam (EPP) is a type of closed-cell bead foam that can be manufactured in many densities, making it ideal for everything from lightweight packaging materials to automotive safety components. The foam offers low emission outgassing of VOCs and comes in anti-static, dissipative, and conductive grades.
EPP is generally made up of beads that are molded together and fused into nearly any shape. This gives them durability and a high strength-to-weight ratio on top of excellent resilience and impact absorption. The foam is also known for its strong thermal insulation, low abrasion, and sound dampening capabilities.
Other uses for EPP foam include:
- Demo and sales cases
- Totes and packaging
- Protective padding in safety products
- Mechanical and industrial applications
Quick Guide to Foam Types
Beaded Polyethylene Foam:
A hard, low-density closed-cell foam that is flexible and easy to fabricate. It’s ideal for the shipping and packaging of sensitive medical devices because of its resiliency, non-abrasiveness, and ability to minimize damage from vibration and liquids. It’s also an excellent insulator and doesn’t off-gas or leave odors.
Crosslinked Polyethylene Foam:
A closed-cell foam that has been chemically crosslinked to give it added properties. It is thicker than beaded polyethylene foam but is also non-abrasive and resistant to chemicals.
Expanded Polystyrene Foam:
A closed-cell foam that is lightweight and rigid. It is also a very good insulator, ideal for shipping pharmaceuticals and other healthcare-related items that rely on strict temperature control. It’s very lightweight, which helps reduce shipping costs.
Expanded Polyethylene Foam:
A highly resilient, closed-cell material that is used for its resistance to mold, mildew, and bacteria. It’s also used for its shock absorption and tear resistance properties.
Expanded Polyurethane Foam:
A lightweight and soft open cell material used for its high shock absorption, flame resistance (meets UL 94 safety standards), and customization capabilities (it can easily be cut into various shapes, etc.).
Ester-Based Polyurethane Foam:
Has a smaller cell structure, making it slightly more rigid and supportive while offering greater tensile strength and durability. It offers great shock absorption but is costly to manufacture and more susceptible to hydrolysis, meaning the material can break down when it comes into contact with water.
Ether-Based Polyurethane Foam:
Has a larger cell structure that allows for more airflow and moisture permeability. This makes the material much more flexible and far more resistant to hydrolysis. It also makes it a much softer and more comfortable surface, all while being less costly to manufacture.
Reticulated Polyurethane Foam:
Reticulation removes the foam’s cell membranes and impurities. When done to a foam such as urethane, it enhances the foam’s natural toughness, increasing the porosity of the foam and making it better at filtering or absorbing liquids.
Browse Our Full List of Foam Materials for Additional Specs, Uses, and Other Technical Information
Options for Foam Fabrication
At Amcon, we’re not only here to help you select the right foam, we’re here to help you bring your next project from concept to completion. This includes employing a range of foam services and capabilities that include product & packaging design to logistics and full-scale foam fabrication.
Many foams can be cut, shaped, molded, and fabricated into a variety of shapes, thicknesses, etc. These customization options allow for each piece of foam to be custom fit any particular application, from packaging to product prototypes.
Some of the many fabrication techniques that can be employed include:
- Precision Water Jet Cutting
- High Speed Die Cutting
- Vertical and Horizontal Contour Cutting
- Abrasive Wire Cutting
- Convoluting
- CNC Routing
- Vacuum and Roll Skiving
- Foam Lamination
