Sandwich panel cores are most commonly made from polypropylene (PP) honeycomb or polymer foam materials such as PET foam. The core sits between two structural skins and determines how the panel distributes load, resists deflection, and manages weight. The right core choice depends on the application, the load conditions, and whether weight or compressive strength takes priority.
Note: This article covers the broader sandwich panel market. Our range at Compoform is limited to PP honeycomb and PET foam cores for commercial vehicles and scaffolding.
The sections below address the most common questions buyers and engineers ask when specifying sandwich panel cores.
What types of materials are commonly used as sandwich panel cores?
The most widely used sandwich panel core materials are polymer foams and thermoplastic honeycombs. Polymer foams include PET foam and polystyrene foam, while thermoplastic honeycombs are typically made from polypropylene (PP). Each core type offers a different balance of weight, stiffness, compressive strength, and cost, making the choice application-specific rather than universal.
Across the broader market, you will encounter several core categories:
- PP honeycomb: A thermoplastic honeycomb structure made from polypropylene. Lightweight, high in compressive strength relative to its mass, and fully recyclable. Widely used in vehicle flooring, scaffolding boards, and structural panel applications.
- PET foam: A closed-cell polymer foam made from polyethylene terephthalate. Offers good stiffness-to-weight performance, excellent surface quality, and strong resistance to moisture and UV degradation. Common in wall panels and cladding applications.
- Polystyrene (EPS/XPS) foam: Low-cost and lightweight, but limited in structural performance and temperature resistance. Used mainly in insulation-focused building panels.
- Other foam types: Various polymer foams appear across the market in different density grades, each tuned for specific load and weight requirements.
Core density is a key specification variable. PET foam, for example, is available in multiple density grades, which allows engineers to tune stiffness and strength for a specific panel thickness and load requirement without changing the overall panel architecture.
How does the choice of core material affect panel performance?
Core material directly controls three performance characteristics: bending stiffness, compressive strength, and panel weight. A denser or more rigid core increases stiffness and load capacity but adds mass. A lighter core reduces weight but may require a thicker panel or heavier skins to compensate for lower structural performance. Getting this balance right is the central engineering decision in sandwich panel design.
Beyond structural performance, core material also affects:
- Moisture resistance: Closed-cell foam cores resist water ingress. Open-cell or fibrous cores can absorb moisture over time, which degrades performance and adds weight in service.
- Temperature behaviour: Thermoplastic cores like PP honeycomb maintain performance across a wide temperature range, which matters for panels exposed to outdoor conditions or industrial environments.
- Recyclability: Thermoplastic cores can be reprocessed at end of life. For European OEMs subject to the EU End-of-Life Vehicles (ELV) Directive, this is a compliance consideration, not just a preference.
- Surface finish compatibility: Some cores bond more readily to specific skin materials, affecting the quality and durability of the skin-to-core interface.
For truck body builders and trailer manufacturers, core selection also has a direct commercial consequence. A panel that is 20 kg lighter per unit translates into measurable payload gain across a fleet. In 2026, that argument extends beyond payload: lighter body structures extend battery range in electric trucks and vans. Every kilogram of structural dead weight reduces range per charge, making weight reduction a range argument, not just a payload argument. EV fleet buyers now raise this as a standard procurement question.
What is the difference between foam and honeycomb sandwich panel cores?
The key difference between foam and honeycomb cores is their internal structure and how that structure handles load. Foam cores are solid and isotropic, meaning they resist load roughly equally in all directions. Honeycomb cores are cellular and directional, with very high compressive strength along the cell axis but lower resistance to in-plane shear. This makes honeycombs better suited to applications with concentrated point loads, while foam cores perform well under distributed loads and provide a more uniform base for surface finishes.
Foam cores: distributed load and surface quality
Foam cores provide a continuous, solid substrate across the full panel face. This makes them well suited to wall panels and cladding where surface flatness and finish quality matter. PET foam, for instance, bonds well to thermoplastic skins and supports a smooth, decorative surface finish. The closed-cell structure also resists moisture absorption, which is relevant for panels used in outdoor or wash-down environments.
Foam cores are available in a range of densities. Lower-density grades reduce panel weight; higher-density grades increase stiffness and compressive resistance. This flexibility makes foam cores a practical choice when you need to tune performance across a product range without redesigning the panel architecture.
Honeycomb cores: high compressive strength at low weight
PP honeycomb cores achieve high compressive strength with very little material mass. The hexagonal cell geometry transfers load efficiently along the cell axis, which is why honeycomb cores are the preferred choice for floor panels, scaffolding boards, and other applications where point loads or concentrated foot traffic are the dominant load case.
The trade-off is that honeycomb cores are directionally sensitive. Load applied perpendicular to the cell axis is handled well; lateral shear across the panel plane relies more heavily on the skins. Panel design must account for this, particularly in applications where the dominant load direction changes.
Which core materials are used in thermoplastic sandwich panels?
Thermoplastic sandwich panels use cores that can be processed, bonded, and recycled within a fully thermoplastic system. The two core materials used in thermoplastic panels are PP (polypropylene) honeycomb and PET (polyethylene terephthalate) foam. Both are compatible with thermoplastic skins such as glass-fibre-PP laminates, and both can be reprocessed at end of life, supporting compliance with the EU ELV Directive for vehicle manufacturers.
PP honeycomb is the standard core for structural applications such as truck body floors and scaffolding boards, where compressive strength and low weight are the primary requirements. PET foam is more commonly used in wall panels and cladding, where surface quality, UV resistance, and dimensional stability take priority over maximum compressive load capacity.
The thermoplastic nature of both core materials matters for the manufacturing process. Unlike thermoset systems, thermoplastic panels can be formed, welded, and recycled using heat-based processes, which simplifies fabrication and supports end-of-life recovery.
What core material is best for lightweight transport applications?
PP honeycomb is the most effective core material for lightweight transport applications. It delivers high compressive strength relative to its mass, which allows panel designers to achieve the structural performance required for truck body floors and trailer walls without the weight penalty of steel or plywood. For transport applications, the combination of low areal weight and high load capacity makes PP honeycomb the practical choice for both floor and wall panels.
The weight advantage is not just a payload argument. For operators transitioning to electric trucks and vans, lighter body structures directly extend battery range per charge. In 2026, EV fleet buyers increasingly specify maximum body weight as a procurement requirement, and composite panels with PP honeycomb cores are one of the most effective tools for meeting that target without compromising structural integrity.
For wall panels in the same vehicle, PET foam cores offer a lighter alternative where compressive load demands are lower. The choice between the two often comes down to the specific load case: floors and load-bearing structures benefit from honeycomb; interior walls and cladding panels can use foam cores at lower weight and cost.
Thermoplastic panels with PP honeycomb cores also outlast plywood in heavy transport service. Industry experience with composite flooring in truck bodies shows service lives of 12 or more years, compared to 3 to 5 years for plywood. Over a 15-year vehicle life, that eliminates two or three replacement cycles. When you factor in panel cost, installation labour, and vehicle downtime, the composite floor is cheaper per year of service even at a higher unit price.
How does core thickness influence sandwich panel strength?
Increasing core thickness is the most efficient way to increase a sandwich panel’s bending stiffness. The core acts as the web of an I-beam, separating the two structural skins. A thicker core places the skins further apart, which increases the panel’s second moment of area and dramatically improves resistance to bending under load. Doubling core thickness increases bending stiffness by a factor of approximately four, while adding very little mass compared to increasing skin thickness.
This relationship means that specifying the right core thickness is often more effective than adding more skin plies. For floor panels in truck bodies and trailers, increasing core thickness from 15 mm to 30 mm delivers a substantial improvement in load capacity. Compoform’s own testing shows that a 30 mm PP honeycomb floor panel sustains an average maximum load of 5,647 N in the tested geometry, compared to 3,240 N for the 15 mm variant, with the same skin specification on both panels.
Core thickness also affects panel weight, but the increase is modest relative to the structural gain. PP honeycomb is low in density, so a thicker core adds relatively little mass. This makes thickness the preferred design lever when you need more structural performance without significantly increasing panel weight.
For scaffolding boards, where the dominant load is applied across the panel width in a plank-style loading scenario, core thickness works together with skin layup orientation to control deflection. An 11 mm PP honeycomb scaffolding panel with a directionally optimised skin layup can achieve EN 12811 load class 4 with no support underneath, demonstrating how core thickness and skin architecture work together rather than independently.
How Compoform Helps You Specify the Right Core
We manufacture thermoplastic sandwich panels with PP honeycomb and PET foam cores for commercial vehicles and scaffolding. Every panel configuration we produce is engineered for a specific application, not selected from a generic catalogue. When you bring us a design challenge, we review your load requirements, assembly process, and end-use environment before recommending a core type, density, and thickness.
Here is what that looks like in practice:
- Core selection: We help you choose between PP honeycomb and PET foam based on your actual load case, not a general rule of thumb.
- Thickness optimisation: We model the structural impact of different core thicknesses so you can hit your performance target at the lowest possible weight.
- Custom dimensions: Panels are available in custom dimensions cut to your exact specification, including large-format panels up to 13,500 mm × 2,950 mm that are not available off the shelf elsewhere in Europe.
- Edge protection: Edge sealing and edge bending are available to protect the core from UV and moisture, which is relevant for truck floors washed down regularly and scaffolding boards used outdoors.
- EV fleet compatibility: If your customers are transitioning to electric vehicles, we can help you quantify the weight reduction achievable with composite panels and translate that into a range-per-charge argument for their procurement teams.
We do not ship panels to spec and move on. We stay involved through integration, flag issues before they reach production, and support you through any iteration your assembly process requires. If you are specifying panels for truck bodies, trailers, or scaffolding boards and want to work through the core selection with an application engineer, get in touch with our team to start the conversation.