Separate the skins
The core holds the two skins apart, increasing the panel's second moment of area and therefore its bending stiffness.
Material overview
What Is PMI Structural Foam?
PMI foam is a rigid, closed-cell structural foam based on polymethacrylimide. It is used as the core of composite sandwich panels, where low weight and stiffness have to work together with elevated-temperature processing.
PMI foam, defined
PMI stands for polymethacrylimide. A PMI structural foam is supplied as blocks or sheets and bonded between composite skins to form a sandwich. The foam is rigid, closed-cell and intended to carry shear rather than in-plane load.
Because the core separates the skins, a thin-skinned panel can reach bending stiffness that would otherwise need a much heavier solid laminate. The core also stabilises the skins against local buckling.
The material is not a single fixed specification. Density, cell structure, mechanical properties, sheet format and heat resistance change with the grade. Those values must come from the current TDS for the exact grade under evaluation.
How the core works
Three jobs in a sandwich panel
Carry shear
Bending and transverse loads put the core in shear. Core shear strength and modulus are therefore central selection values.
Stabilise the skins
By supporting the skins continuously, the core delays local buckling and lets thin skins work efficiently.
Selection
What decides the grade
- Load case. Compressive, shear and bending demands, including local loads at inserts and fasteners.
- Stiffness target. How much deflection the panel can accept under service load.
- Weight budget. The trade between core density and structural performance.
- Process cycle. Cure temperature, pressure, resin system and whether the core is co-cured or bonded.
- Environment. Moisture, temperature and repeated loading over the intended service life.
- Geometry and finish. Sheet thickness, machined profiles, thermoformed curvature and surface quality.
This site does not publish values for these factors until they are confirmed in the current TDS.
Processing
From block to core
PMI cores are commonly machined to the panel geometry and can be thermoformed into curved shapes. They are used in prepreg layups, vacuum bag and autoclave cycles, and resin infusion or moulding processes, depending on the resin system and the grade.
Processing limits are grade-specific. Before committing a cure cycle, confirm the allowed temperature, pressure and time from the current TDS, and test the actual layup where the process is new.
Questions
PMI foam FAQ
Is PMI foam a structural foam?
Yes. PMI foam is used as a structural core in composite sandwich panels, where it carries shear and stabilises the skins.
Is PMI foam closed-cell?
Yes. PMI structural foam has a closed-cell structure, which helps limit resin uptake during infusion and bonding.
Can PMI foam be used in autoclave curing?
PMI foams are selected for elevated-temperature processing, including prepreg and autoclave cycles. Suitability depends on the grade and the exact cycle, so confirm the current TDS before release.
Can PMI foam be CNC machined?
PMI cores can generally be machined and thermoformed. Tooling, feeds and surface finish depend on the grade; confirm the recommended process with the technical data.
Which density should I choose?
Density selection depends on the load case, stiffness target, weight budget, panel geometry and process. Values are grade-specific, so request the TDS for the grades you are comparing.
Is PMI foam the same as polymethacrylimide foam?
Yes. PMI is the standard abbreviation for polymethacrylimide, the polymer family used in PMI structural foams.
Need data for a specific grade?
Tell us the application and the grade or series you are evaluating. We will confirm what technical data can be provided.