Resin Uptake in ROHACELL® PMI Foam

Resin uptake in Rohacell
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Resin uptake is the amount of liquid resin that interacts with and penetrates the surface of a foam core during composite manufacturing. In lightweight composite structures, resin uptake has a direct effect on final part weight, stiffness, surface quality, and process repeatability.

Rohacell polymethacrylimide foam is engineered to exhibit extremely low and highly predictable resin uptake. This behaviour is a direct result of its closed cell structure, fine and uniform microcell morphology, and tightly controlled manufacturing process. These characteristics make Rohacell a preferred core material for precision composite structures in aerospace, motorsport, UAV, medical, and industrial applications.
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What resin uptake means in composite manufacturing
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Every foam core absorbs some resin during layup and cure. The amount absorbed depends on material structure, surface condition, processing pressure, temperature, and resin viscosity. Excessive resin uptake adds mass without contributing useful structural performance and can introduce variability in stiffness and bond quality.

In high performance composite design, controlling resin uptake is essential. Rohacell is specifically designed to minimise this interaction while still providing a strong and reliable skin to core bond.

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Why Rohacell has low resin uptake

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Rohacell has a true closed cell microstructure. Individual cells are discrete and not interconnected, preventing resin from flowing through the core volume. Resin interaction is therefore limited to surface wetting and very shallow surface penetration.

The foam’s microcell structure is extremely fine and consistent, reducing the number of fractured or open cells that could otherwise act as resin pathways. Rohacell sheets also have a naturally dense surface skin, which further limits surface porosity.

During composite cure cycles, Rohacell maintains dimensional and structural stability under heat and pressure. The foam does not collapse, soften, or microcrack, preventing the formation of resin rich zones or internal resin channels.

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How resin uptake affects composite performance

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Low resin uptake reduces overall component weight and allows designers to meet mass targets with confidence. Because absorption is predictable, laminate weight and resin consumption can be accurately estimated during the design stage.

Surface quality is improved because resin does not soak deeply into the core. Rohacell supports smooth laminate surfaces even under thin composite skins.

Bond performance is reliable because sufficient resin wets the immediate surface of the foam to create strong adhesion without flooding the core. Mechanical properties such as shear strength and compressive strength remain stable across the part.

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Resin uptake across Rohacell grades

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Rohacell is available in multiple grades and densities, all engineered to maintain low resin uptake.

General purpose grades such as IG and IG-F offer very low absorption and are widely used in aerospace interiors, fairings, housings, motorsport structures, and medical components.

WF grades feature extremely fine cell structures that further reduce resin uptake, making them suitable for ultra lightweight laminates and thin skins.

High temperature grades such as HERO and HT retain closed cell stability during elevated temperature cure cycles, preventing increased resin penetration under autoclave conditions.

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Processing factors that influence resin uptake

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Although Rohacell inherently limits resin absorption, processing variables still influence results. These include resin viscosity, laminate pressure, cure temperature, and surface condition after machining.

Prepreg systems offer very consistent resin films and are commonly paired with Rohacell for maximum repeatability. Wet layup and infusion processes also perform well when resin content is controlled and surface preparation is appropriate.

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Where controlled resin uptake matters

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Rohacell is used in applications where resin control directly influences performance and certification. These include aerospace composite sandwich structures, motorsport aerodynamic components, UAVs, space structures, precision RF components, and lightweight industrial tooling.

In these environments, predictable resin uptake supports consistent weight, stiffness, fatigue performance, and quality control.

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Summary of resin uptake behaviour

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Rohacell exhibits low, controlled, and repeatable resin uptake due to its closed cell PMI structure. Resin interaction is limited to surface wetting and bonding interfaces, ensuring weight efficiency, process stability, and reliable mechanical performance.

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