Nickel foam selection starts with understanding what each specification describes. PPI describes a pore-count convention, thickness describes the sheet depth, and porosity describes the proportion of void space. Read these values together when comparing samples. A PPI number alone cannot identify the complete structure or predict how a foam will perform in your application.
What PPI tells you
PPI means pores per inch. It is commonly used to describe the number of pores along a linear distance in a foam. Within a comparable product family and counting method, a higher PPI generally indicates a finer structure.
The counting convention matters when comparing suppliers. Metal-foam manufacturer Recemat describes PPI as a non-standardised designation and supplies pore-count ranges for its grades. A nominal number should therefore be read alongside the supplier's description or measurement method, rather than treated as an exact universal specification. Recemat specifications
Why PPI is not a guaranteed opening size
An open-cell foam contains a three-dimensional network, including cells and the openings that connect them. The cell dimensions and the connecting openings need not be the same. Sumitomo Electric's Celmet product information lists cell count, average pore diameter and average window diameter separately. Those are specifications for its own products, but the distinction is useful when reading any foam datasheet. Celmet product information
Dividing 25.4 by a PPI number gives a length based on that linear count. It does not establish the measured clear opening through which a fluid or particle passes. For example, 25.4 divided by 100 is 0.254 mm. That arithmetic alone is not evidence that a nominal 100 PPI foam has a guaranteed 0.254 mm pore opening or filtration rating.
If opening size matters to the project, a measured pore or window description and its test method are more useful than a conversion table without a stated basis.
Porosity and thickness answer different questions
Porosity is the void fraction of a defined bulk volume. Two foams can have similar porosity but different cell sizes. Recemat's specifications distinguish porosity and density from pore size, illustrating why these should remain separate entries in a comparison. Recemat specifications
Thickness describes the depth of the sheet. It is useful to distinguish thickness as supplied from thickness after rolling, pressing or installation. Sumitomo Electric lists rolling among its foam-processing methods, so a thickness value should retain its processing context. Celmet processing information
Areal mass, expressed as mass per sheet area, is another practical comparison value. Two samples with the same nominal PPI and thickness should not automatically be assumed to contain the same amount of metal.
Compare samples around the job they need to do
For an electrode project, first identify whether the foam will be used bare, carry a coating or support another component. Compare candidate samples under the same preparation and assembly conditions. Useful observations can include coating distribution, electrical contact and whether the intended fluid paths remain accessible after processing.
For a filtration project, start with the particles and fluid involved. A nominal PPI value does not establish removal efficiency. Performance should be evaluated with the intended flow, sample support and sealing arrangement.
For a part that will be compressed, record its dimensions before and after assembly. The supplied sheet and the installed component are different measurement states. Our nickel foam manufacturing guide explains the material structure, while the alkaline electrolysis guide covers application-specific evaluation in more detail.
A simple starting point for an enquiry
You do not need a complete specification to start a discussion. A brief description of the application, a reference sample or a photograph can help establish which details to compare next. If you already know the preferred thickness, sheet size or PPI, you are welcome to include them.
Explore our nickel foam range, or contact HuiRui to discuss material options. Any proposed specification can then be checked against the actual material and the needs of your project.