PORON Cushioning Blog Blog

PORON Cushioning Blog

Open Cell vs Closed Cell Cushioning Foams – Tips for Choosing the Best Material for Your Product Design

Posted by Dave Sherman on Thursday, April 7th, 2011 | 3 Comments »

Many customers are often surprised when we explain to them that all PORON® Performance Cushioning Materials are open cell polyurethane foams.  It seems that the standard cushioning foams that they see on the market are typically closed cell EVA foams or closed cell polyurethane foams.

In fact, the open cell nature of PORON Cushioning foams is one of the material properties which help to make PORON Materials have the best resistance to compression set (C-Set) or for the non-foam geeks out there: resistance to break down after multiple uses.

Open Cell vs Closed Cell Foam

Ask youself…What do you need: A tennis ball or a spring?

EVA foams, commonly used in insoles and sports padding, are closed cell foams, meaning that all the bubbles of trapped air in the foam are complete bubbles, with cell walls all around, like a million balloons all stuck together. This kind of foam gets most of its properties from the air trapped inside the bubbles. When the foam is compressed, say when you’re walking on an insole or when you land on your elbow pad, the air inside the bubbles is compressed, and the return force is caused by the decompression of the air. This behavior is just like the behavior of a tennis ball, which gets its bounce from the air inside the ball.  Like a tennis ball, the air eventually leaks out of the cell, and the foams go flat, or “take a set” in foamese.  That means the foam insole is less comfortable on the next step, or less protective on the next hit.

Closed Cell Foam: Before and After Long Term Compression (C-Set)

Closed Cell Foam Under Compression

PORON Cushioning materials are an open cell foam, which has little connections or portals between the cells that allow air flow between them.  So PORON materials are not dependent on the air for their properties, but instead on the properties of the materials in their cell walls. They operate more like spring, and return to their original position after being compressed, time after time because the air moves freely in and out of each cell.

Open Cell Foam: Before and After Long Term Compression (C-Set)

open cell foam before and after long term compression

Choosing an open cell vs closed cell foam for your product design

Being closed cell offers some advantage and disadvantages in applications. The foams can be very light, as their cell walls can be very thin, but are usually stiff because of the incompressibility of the air inside them They can also be better at resisting liquid penetration.

Likewise, in addition to being resistant to taking a set, open cell foams have some other advantages, like being breathable and soft (better Compression Force Deflection – CFD). The table below summarizes some of the advantages (marked with an A) each foam has.

Foam Properties

Measures

Closed

Open

CFD Softness/Conformability   A
Compression Set Resistance Life of Properties   A
Anti Microbial Integral Coating    
Breathability MVTR-Yes/No   A
Water Absorption % Uptake After Some Time A  
Washability Cycles at Setting A  
Closed/Open Cell      

So as you design something that will use a foam, ask yourself what are the most important properties you want. If you want light weight and great washability, then use a closed cell foam. If you want reliability over time, softness and breathability, choose PORON? Performance Cushioning Materials.

open cell SEM images

Dave Sherman

Dave Sherman

Technical Design Solutions Manager at XRD® Impact Institute
Dave Sherman is the Innovation Leader at the XRD® Impact Institute - the research, design and testing facility of XRD® Impact Protection Technology. His experience involves a wide variety of foams including polyethlyene, polypropylene, EVA, rubber, polyurethane, silicone, and melamine. He has a Chemical Engineering degree from MIT and an MBA from RPI, as well as over 30 years of experience in the business of developing material solutions to meet demanding customer needs.

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