This article covers the broader sandwich panel market. Compoform’s range is limited to PP honeycomb and PET foam cores for commercial vehicles and scaffolding.
The core in a sandwich panel carries shear loads between the two face skins, keeps those skins separated at a fixed distance, and resists compression perpendicular to the panel surface. Without a structurally capable core, the skins buckle independently and the panel loses most of its load-bearing capacity. The sections below answer the most common technical questions about core materials, from how they affect stiffness to which type performs best under impact.
How does the core material affect a sandwich panel’s stiffness?
The core material determines a sandwich panel’s bending stiffness by controlling how far apart the two face skins are held and how effectively shear forces transfer between them. A stiffer, denser core keeps the skins working together as a unit, which multiplies the structural contribution of the skins far beyond what either skin could achieve alone.
The structural logic is similar to an I-beam: the flanges (skins) carry tension and compression, while the web (core) transfers shear. If the web is weak or soft, the flanges deflect independently and the beam collapses. In a sandwich panel, a core that deforms under shear allows the skins to slide relative to each other, which destroys bending stiffness even if the skins themselves remain intact.
Core thickness also plays a direct role. Increasing panel thickness by adding core depth raises bending stiffness significantly, because stiffness scales with the cube of the distance between the skin centroids. This is why relatively thin skins bonded to a thick, lightweight core can outperform a much heavier solid plate in bending resistance per unit of weight.
What types of core materials are used in composite sandwich panels?
Across the broader sandwich panel market, the most common core materials are polymer foams, honeycomb structures, and natural or engineered solid materials. Each category offers a different balance of density, shear strength, compressive resistance, and cost. The right choice depends on the load type, operating environment, and production method.
Polymer foam cores are the most widely used category. Polypropylene (PP) foam and PET foam are thermoplastic options that combine low density with good compressive and shear properties. They are compatible with thermoplastic manufacturing processes and are fully recyclable, which is increasingly relevant under the EU End-of-Life Vehicles (ELV) Directive for commercial vehicle manufacturers and their applications.
Honeycomb cores are structured arrays of cells, typically hexagonal, that provide very high stiffness-to-weight ratios. PP honeycomb is a thermoplastic option used in demanding structural applications such as truck body floors and scaffolding boards, where compressive strength and shear resistance under point loads are priorities.
Other core types found across the market include balsa wood, aluminium honeycomb, and mineral wool, though these are associated with specific sectors such as marine, aerospace, and fire-rated building panels, respectively, and are not part of every manufacturer’s range.
How does core density influence panel weight and load capacity?
Higher core density increases both the panel’s weight and its structural capacity. A denser core contains more material per unit volume, which raises compressive strength, shear strength, and resistance to local indentation. The trade-off is a heavier panel, so selecting the right density means matching structural requirements to the minimum weight that meets them.
For truck body builders and trailer manufacturers, this trade-off has direct commercial consequences. Every kilogram of structural dead weight in a vehicle body reduces the payload capacity available for revenue-generating cargo. In electric trucks and vans, the impact goes further: heavier body structures reduce battery range per charge, which is now a standard procurement question from EV fleet buyers in 2026. Weight reduction is no longer just a payload argument — it is a range argument.
PP foam cores, for example, are available across a range of densities. Lower-density foam suits wall cladding applications where compressive loads are modest. Higher-density foam or PP honeycomb is specified for floor panels and scaffolding boards where point loads and repeated dynamic loading demand greater compressive resistance. Selecting the lowest density that meets the structural requirement keeps the panel as light as possible without compromising performance.
What happens to a sandwich panel when the core fails?
When the core of a sandwich panel fails, the panel loses its ability to transfer shear between the skins, and the two face skins begin to act as independent thin plates rather than as a composite structure. This causes a sudden and dramatic loss of bending stiffness, often followed by visible wrinkling or buckling of the compressed skin.
Core failure can take several forms depending on the load type and core material:
- Shear failure occurs when the core cannot transfer the shear forces generated by bending. The skins slide relative to each other, and the panel deflects far beyond its design limit.
- Compressive failure happens under concentrated point loads, such as a foot load on a scaffolding board or a fork tine on a truck floor. The core crushes locally, creating a permanent indentation and reducing the panel’s load-bearing capacity in that area.
- Delamination is the separation of the skin from the core at the adhesive interface. Once a skin detaches, it contributes nothing to the panel’s structural performance, even if the skin itself is undamaged.
In practice, well-designed sandwich panels are engineered so that the core and skin fail at similar load levels, avoiding a situation where one element is significantly over-specified relative to the other. For scaffolding applications in particular, resistance to localised compressive failure is a primary design criterion, since workers and equipment create concentrated loads across the board’s surface.
How does core material choice differ between thermoplastic and thermoset sandwich panels?
The core material choice is closely linked to the manufacturing process. Thermoplastic sandwich panels are produced using heat and pressure, which means the core must survive processing temperatures without degrading. Thermoset panels are cured at lower temperatures using resins, which opens the door to a wider range of core materials that cannot withstand thermoplastic processing conditions.
In thermoplastic panels, PP honeycomb and PET foam are the standard core options. Both materials are compatible with the heat and pressure of thermoplastic lamination, and both are fully recyclable at end of life. This recyclability is a compliance consideration for European OEMs subject to the EU ELV Directive, which requires vehicle manufacturers to demonstrate that a high proportion of vehicle materials can be recovered and recycled.
Thermoset panels, by contrast, are commonly produced with balsa wood, aluminium honeycomb, or other materials that suit lower-temperature curing processes. However, thermoset panels are not recyclable in the same way, because the resin matrix cannot be remelted and reprocessed. For manufacturers facing increasing pressure under the EU Corporate Sustainability Reporting Directive (CSRD), this distinction is becoming a more active factor in material selection decisions.
The practical implication for truck body builders and trailer manufacturers is that thermoplastic panels offer a recyclability advantage that thermoset alternatives cannot match, without sacrificing structural performance in the applications where they are specified.
Which core material is best for high-impact applications?
For high-impact applications, PP honeycomb cores consistently outperform foam cores in compressive strength and resistance to localised impact damage. The structured cell geometry of a honeycomb distributes impact energy across multiple cell walls, which limits the depth and spread of damage compared to a foam core of equivalent density.
In scaffolding boards and truck body floors — two of the most demanding impact environments in commercial applications — PP honeycomb provides the compressive resistance needed to handle repeated point loads without permanent deformation. The skin architecture also plays a role: a triaxial glass-fibre layup (such as a 90-0-90 configuration) distributes tensile loads in multiple directions, which improves the panel’s ability to absorb and spread impact forces rather than concentrating them at a single point.
Skin reinforcement technology further raises the ceiling on impact performance. Continuous fibre-reinforced tape, for example, generates significantly higher impact resistance compared to standard composite skins, making it relevant for applications where impact events are frequent or severe.
The right answer for any specific application depends on the nature of the impact (distributed vs. point load), the frequency of loading, and the acceptable level of permanent deformation. A scaffolding board must survive repeated foot traffic and tool drops without visible damage. A truck body floor must resist fork tine loads and pallet drops across a working life measured in years, not months.
How Compoform Supports Core Selection for Your Application
We work with two core materials — PP honeycomb and PET foam — specified across a range of densities to match the structural and weight requirements of your application. Rather than offering a standard panel and asking you to adapt your design around it, we review your load requirements, operating environment, and assembly process before recommending a configuration.
For truck body builders and trailer manufacturers, this typically means:
- Selecting core density to meet floor load requirements while keeping panel weight as low as possible — directly supporting payload capacity and, for electric vehicle fleets, battery range per charge
- Specifying skin architecture (cross-ply, 2-ply, or 4-ply glass-fibre) to match the direction and magnitude of the loads your panels will carry
- Producing panels in custom dimensions up to 13,500 mm × 2,950 mm, eliminating joints that create weak points in large floor or wall assemblies
- Providing edge sealing and edge bending where panels are exposed to wash-down cycles or outdoor conditions, protecting the core from moisture ingress over the panel’s service life
For scaffolding manufacturers, we can reference our own test data: a 10.5 mm Compoform panel achieved EN 12811 load class 4 with no support underneath — a result that comes from the combination of PP honeycomb core density, skin layup, and panel geometry working together, not from any single element in isolation.
If you are specifying a panel for a new application or reviewing an existing design, speak with our engineering team about the load case, and we will work through the core and skin configuration with you before anything goes into production.