Beyond Density: Characterizing Open and Closed Cell Content in Rigid Foams

Abstract: Ethylene–vinyl acetate (EVA) and expanded polyethylene (EPE) foams are widely utilized in packaging, thermal insulation, and acoustic applications due to their favorable mechanical and physical properties. In addition to visual and structural characteristics, the ratio of open and closed cells within the foam significantly influences key performance metrics such as moisture resistance, thermal conductivity, cushioning behavior, and sound attenuation. This application note outlines a gas pycnometer-based methodology for quantifying open and closed cell content in EVA and EPE foams. Accurate measurement of these parameters enables more reliable prediction of material performance and supports informed material selection for specific application requirements.

Keywords: Rigid foam, Open cell content, Closed cell content, Gas pycnometer, ASTM D6226, ISO 4590

 

Product	BetterPyc 380
Industry	Building Materials, Chemicals, Polymers and Plastics
Sample	EVA foam, EPE foam
Measurement Type	Density
Measurement Technology	Powder Characterization, Gas Displacement Method

 

Jump to a section: 

• Introduction
• Instrument
• Experimental
• Conclusion

 

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Introduction 

 

Rigid foams are extensively used in industries such as construction, automotive, aerospace, and packaging due to their lightweight structure and versatile performance characteristics. While density has traditionally been the primary metric for evaluating foam quality, analysis of the cell structure provides more comprehensive insights into the material's functional properties.

In rigid foam materials, open cell content refers to interconnected pores that permit the passage of gas and fluids, whereas closed cell content refers to isolated pores that are sealed off from the surface, resulting in reduced permeability. Open cell foams generally offer higher breathability and water absorption, while closed cell foams provide enhanced waterproofing and insulation.

Precise quantification of open and closed cell content is essential for evaluating key performance attributes such as mechanical integrity, thermal efficiency, and long-term durability. These measurements play a crucial role in quality assurance, material design refinement, and process optimization, ensuring that the foam structure aligns with the functional requirements of its intended application.

 

Figure 1. Structure of rigid foam material

 

Instrument and Sample Description

 

Experimental Data Analysis and Comparison

 

Table 1 summarizes the measurement conditions used during testing, while Table 2 presents the basic physical parameters of the EVA and EPE foam samples — including geometric volume, mass, and specific gravity — which serve as input data for subsequent analysis with the BetterPyc 380.

 

Table 1. Measurement conditions

Parameter	Value	Parameter	Value
Temperature	25℃	Sample cup	100 mL
Gas type	Nitrogen	Equilibrium	0.01 psig/min
Purge cycle	10	Purge pressure	3 psig
Analysis cycle	3	Analysis pressure	3 psig

 

Table 2. Foam sample information

Sample	Geometric Volume (cm3)	Mass(g)	Specific Gravity
EVA foam	30.9850	0.3820	0.92
EPE foam	52.4031	0.5115	0.95

 

As shown in Table 3, the open and closed cell contents of EVA and EPE foams were determined using the gas displacement method, an efficient and reliable technique for characterizing foam cell structures. The EPE foam exhibited a significantly higher open cell content (96.33%) and a lower closed cell content (2.64%) compared to EVA foam (88.42% and 10.24%, respectively), indicating that EPE possesses a more porous and permeable internal structure.

 

Quantifying the open and closed cell contents of EVA and EPE foams provides valuable insight into their functional characteristics. Materials with higher open cell content, such as EPE, generally allow greater airflow, flexibility, and acoustic absorption. In contrast, materials with higher closed cell content, such as EVA, provide superior airtightness, mechanical strength, and thermal insulation. These structural differences directly influence the performance and suitability of foam materials for specific applications.

 

Additionally, the low standard deviations (≤ 0.08%) observed across all measurements highlight the excellent repeatability and precision of the BetterPyc 380, confirming its reliability for accurate foam characterization.

 

Table 3. The cell content results of foam specimens

Sample	NO.	Open Cell Content (%)	Std.Dev.  (%)	Closed Cell Content (%)	Std.Dev.  (%)
EVA foam	1	88.35	0.06	10.32	0.06
	2	88.42		10.24
	3	88.50		10.16
	Average	88.42		10.24
EPE foam	1	96.44	0.08	2.53	0.08
	2	96.32		2.65
	3	96.23		2.74
	Average	96.33		2.64

 

Conclusion 

 

This study demonstrates that the BetterPyc 380 gas pycnometer provides a reliable and standardized method for characterizing the open and closed cell contents of rigid foams in accordance with ASTM D6226 and ISO 4590. Quantitative analysis of EVA and EPE foams revealed distinct structural differences: EPE possesses a predominantly open-cell structure, while EVA retains a higher closed cell content — each contributing to unique performance advantages.

 

These measurements provide insights beyond conventional density metrics, offering a deeper understanding of foam morphology and its influence on functional properties such as permeability, insulation, and mechanical strength. Incorporating open and closed cell analysis into routine quality control and R&D workflows enables manufacturers to optimize formulations, enhance product performance, and ensure consistency across production batches.

 

About the Authors

Feiqing Shen Application Research Lab, Bettersize Instruments Ltd.

 

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