Sandwich panels used in modular building construction most commonly fall into two categories: foam-core panels for wall and ceiling applications, and honeycomb-core panels for floors and load-bearing surfaces. The right panel type depends on the structural demands of the specific surface, the required thermal performance, and the weight budget of the module. The sections below unpack each of these questions in detail.

Note: This article covers the broader sandwich panel market as it applies to modular construction. Our range at Compoform is focused on PP honeycomb and PET foam cores for commercial vehicles and scaffolding.

Which types of sandwich panels are most common in modular construction?

The most common sandwich panels in modular building construction are foam-core panels for walls and ceilings, and honeycomb-core panels for floors and structural decks. Both types share the same basic architecture: two stiff facing skins bonded to a lightweight core. The core carries shear loads and separates the skins to create bending stiffness, while the skins carry tension and compression.

In modular construction specifically, panels serve three distinct roles, each with different performance priorities:

• Wall cladding panels need good bending stiffness in both directions, a finished surface, and resistance to weathering and UV exposure
• Floor panels need high compressive and bending strength to handle point loads, foot traffic, and equipment
• Structural or infill panels need dimensional stability, low weight, and compatibility with the module’s connection system

Thermoplastic composite panels have grown in use across all three roles because they combine low weight with long service life and resistance to moisture, which is a persistent problem with plywood-based modular construction. You can explore the full range of modular construction panel applications on our applications page.

What core materials are used inside modular building panels?

The core materials most commonly used inside modular building sandwich panels are polypropylene (PP) foam, PP honeycomb, and polyurethane (PU) foam. Each core type offers a different balance of weight, stiffness, compressive strength, and thermal performance. The choice of core material is one of the most consequential decisions in panel design.

PP foam cores

Oriented PP foam is available in a range of densities, typically from 40 to 140 kg/m³. Lower-density grades keep weight down and provide adequate stiffness for wall panels. Higher-density grades add compressive strength for applications where the panel must resist point loads. The oriented structure of the foam improves mechanical properties compared to standard isotropic foams, and PP foam is fully thermoplastic, which supports recyclability under the EU End-of-Life Vehicle (ELV) Directive and similar frameworks.

PP honeycomb cores

PP honeycomb cores offer a higher strength-to-weight ratio than foam for a given thickness. The tubular cell structure resists compressive loads efficiently, making honeycomb the preferred core for floor panels where concentrated loads are common. A 140 kg/m³ PP honeycomb core, for example, delivers compressive performance well above what a foam core of the same density would achieve. The trade-off is that honeycomb cores are less forgiving when panels are cut or drilled on site, because open cells at cut edges need sealing to prevent moisture ingress.

PU foam cores

Polyurethane foam is widely used in the broader construction panel market, particularly where thermal insulation is the primary requirement. PU foam has good thermal resistance values but is thermoset, meaning it cannot be remelted or recycled in the same way as thermoplastic alternatives. For modular builders with sustainability reporting obligations under the EU Corporate Sustainability Reporting Directive (CSRD), this distinction is becoming a more active procurement consideration.

What are the skin or facing materials on modular sandwich panels?

The facing skins on modular building sandwich panels are most commonly glass-fibre-reinforced thermoplastic laminates, steel, or aluminium sheet. The skin material determines the panel’s surface finish, impact resistance, and how it connects to the module frame. For thermoplastic composite panels, skins typically contain 66 to 67% glass fibre by content, which gives them high stiffness relative to their weight.

Skin architecture matters as much as skin material. A cross-ply (CP) layup, where fibres alternate between 0° and 90° orientations, equalises mechanical properties in both directions. This makes the panel suitable for installation in either orientation without a preferred loading axis. A unidirectional or multi-ply layup concentrates strength along a specific axis, which is useful when the dominant load direction is known, such as across the width of a scaffolding plank or along the span of a floor panel.

Surface finish options include:

• White PET film: provides a clean, finished decorative surface with controlled gloss and colour properties, suitable for interior wall cladding
• Anti-skid surface: a textured black finish bonded to the outer skin, used on floor panels and working platforms where slip resistance is required
• Painted or coated steel or aluminium: common on metal-faced panels used in external cladding or fire-rated assemblies

UV resistance is a relevant specification for any panel used in external or semi-exposed applications. Glass-fibre thermoplastic skins with PET film surfaces can achieve over 22,000 hours of UV resistance in accelerated weathering tests conducted to ISO 4892, which covers most practical service life requirements for modular building applications.

How do thermoplastic composite panels differ from metal-faced panels in modular buildings?

Thermoplastic composite sandwich panels are significantly lighter than metal-faced panels of equivalent stiffness, and they do not corrode. Metal-faced panels, typically steel or aluminium skins over a foam core, offer higher surface hardness and are often preferred where fire performance or impact from heavy equipment is the primary concern. The right choice depends on the application and the module’s structural system.

The weight difference is the most commercially significant distinction. A thermoplastic composite wall panel can weigh substantially less than a steel-faced equivalent of the same thickness. In modular construction, this weight saving compounds across every panel in the module, reducing crane lift loads, transport costs, and foundation requirements. For modular units that are relocated repeatedly, the cumulative benefit of lighter panels is considerable.

Corrosion resistance is the second major differentiator. Steel-faced panels require edge protection and surface coatings to prevent rust, particularly in humid or coastal environments. Thermoplastic composite panels do not corrode, and with proper edge sealing, they resist moisture ingress at cut edges as well. This reduces maintenance requirements over the module’s service life.

Metal-faced panels do hold advantages in specific scenarios:

• Where fire classification to EN 13501-1 requires non-combustible facing materials
• Where surface hardness must resist mechanical damage from forklifts or heavy tools
• Where the panel must serve as a structural diaphragm in the building’s lateral load system

For most internal wall, ceiling, and floor applications in modular construction, thermoplastic composite panels offer a better weight-to-performance ratio and lower total cost of ownership over the module’s life.

What performance standards must sandwich panels meet for modular construction?

Sandwich panels used in modular building construction must meet performance standards covering structural load capacity, fire reaction, thermal performance, and dimensional stability. The applicable European standards depend on the panel’s role in the structure and the building’s use classification.

Key standards relevant to modular construction panels include:

• ISO 14125: bending strength and flexural modulus testing for composite panels
• EN ISO 527: tensile strength and modulus testing for skin laminates
• EN 12667: thermal conductivity measurement, relevant for panels used in thermally insulated envelopes
• EN 13501-1: fire reaction classification, required for panels in occupied buildings
• EN 12811: structural performance standard for working platforms and scaffolding, applicable to floor panels used in temporary modular structures

For floor panels specifically, load class certification under EN 12811 provides a clear, testable benchmark. A panel that achieves load class 4 under EN 12811 without additional subframe support demonstrates structural self-sufficiency, which simplifies the module’s floor assembly and removes a production step for the manufacturer.

Dimensional tolerances are also a practical performance requirement. Modular construction relies on panels fitting precisely into prefabricated frames. Panels with tight thickness and length tolerances reduce on-site adjustment and rework. Maximum panel dimensions are a relevant specification for modular builders working with large floor or wall sections, since fewer joints mean fewer potential failure points and faster assembly.

When should modular builders choose composite panels over conventional panel options?

Modular builders should choose composite sandwich panels over conventional options when weight, service life, and moisture resistance are more important than upfront material cost. Composite panels consistently outperform plywood and metal alternatives on total cost of ownership when the full service cycle is considered, not just the purchase price.

The clearest case for composite panels is in floor applications. Plywood floors in modular units typically require replacement every three to five years under regular use. A composite floor panel, by contrast, can last twelve or more years in comparable service conditions, eliminating two or three replacement cycles over the module’s life. When you account for panel cost, installation labour, and the downtime involved in taking a module out of service for floor replacement, the composite option is cheaper per year of service, even at a higher unit price.

Composite panels also make sense when the module will be relocated multiple times. Every kilogram saved in the panel structure reduces transport costs and crane requirements at each move. For modular builders supplying temporary accommodation, site offices, or relocatable infrastructure, this weight argument is directly commercial.

Conventional options remain competitive in specific situations:

• Single-use or very short-life modules where the replacement cycle argument does not apply
• Applications where fire classification requirements mandate non-combustible materials throughout
• Projects where the procurement team has no flexibility to qualify a new material within the project timeline

For most mid-volume modular construction applications in Europe, the combination of weight reduction, long service life, and moisture resistance makes composite sandwich panels the stronger long-term choice.

How Compoform Supports Modular Panel Specification

We manufacture thermoplastic sandwich panels to custom specifications for modular construction applications, with a focus on floor panels and wall cladding where weight, durability, and dimensional precision matter most. Our production line handles panels up to 13,500 mm × 2,950 mm × 150 mm, which means large floor sections can be produced as a single panel rather than multiple joined pieces.

Here is what working with us on a modular panel project looks like in practice:

• Core selection: We work with PP honeycomb and PET foam cores. For floor panels carrying concentrated loads, PP honeycomb at 140 kg/m³ delivers the compressive performance needed for self-supporting floor assemblies. For wall cladding, PP foam in lower density grades keeps weight down without sacrificing bending stiffness.
• Skin configuration: You specify the number of plies, fibre orientation, and surface finish. Cross-ply skins suit wall panels installed in either orientation. Anti-skid surfaces are available for floor panels used as working platforms.
• Dimensional precision: Panels are produced to your exact dimensions, with tight tolerances that fit directly into your module frame without on-site trimming.
• Edge protection: Edge sealing and edge bending are available to protect the core from moisture, which is relevant for floor panels washed down regularly or used in exposed environments.
• EN 12811 performance: A 10.5 mm Compoform panel has achieved EN 12811 load class 4 with no support underneath, based on our own testing. We can share the test data and discuss whether a similar configuration suits your floor load requirements.

We review your design before production, not after. If your panel configuration has a potential issue with edge loading, skin orientation, or connection detail, we flag it at the specification stage, before it becomes a problem on the assembly line. To discuss your modular panel requirements and get a configuration recommendation, contact our engineering team directly.

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