Panel Sandwich Construction Guide for RV Interior | BIGBAHN Factory Wholesale OEM

According to 2026 market research, PET core sandwich panels are rated the top-choice core material, and PET foam board as the core material is accelerating adoption across European RV OEMs.

A panel sandwich is a three-layer composite board consisting of two rigid face sheets bonded to a lightweight core material through adhesive hot-press lamination, where the core carries shear loads and thermal insulation while the faces handle bending and impact forces. In modern RV manufacturing, PET foam core sandwich panels are fully replacing traditional timber-frame construction, with their 100% closed-cell structure delivering zero water absorption and full recyclability, weighing 30–50% less than conventional plywood.

This article covers sandwich panel structural principles, core material comparison (PET vs XPS vs honeycomb), ECE R118 fire compliance, REACH formaldehyde limits, selection guidelines, and wholesale/OEM partnership pathways.

What Is a Panel Sandwich?

The core design philosophy of sandwich panels originates from aerospace composite mechanics — achieving maximum bending stiffness with minimum material mass. 

The structure consists of three layers: top and bottom face sheets, a middle core material, and adhesive layers that bond them into a single unit. Face sheets are typically high-strength thin boards such as laminate panels, aluminium, or glass-fibre reinforced thermoplastic sheets, handling tensile/compressive stress and bending edge loads; the core uses low-density materials such as PET foam board, XPS extruded foam, or PP honeycomb, handling shear transfer and thermal insulation.

This "high-strength skin + low-density core" combination gives sandwich panels a stiffness-to-weight ratio far exceeding monolithic solid boards of equal mass.

Mechanically, the sandwich panel works on the "I-beam principle": the face sheets act as I-beam flanges under axial tension/compression, while the core acts as the web under transverse shear. 

When external force hits the panel surface, the top face compresses and the bottom face stretches, and the core transfers load from one face to the other through shear deformation while maintaining the gap between them — the larger the gap, the greater the moment of inertia and bending strength. 

This is why a 20mm sandwich panel can be several times stronger than a 5mm solid board while weighing less.

In RV applications, this means walls, roofs, and floors can meet structural requirements while significantly reducing weight, directly translating to increased payload capacity.

PET Foam vs XPS vs Honeycomb

The core material decision for RV sandwich panels centers on three options, each with distinct trade-offs across structural strength, thermal insulation, moisture resistance, weight, and cost. 

PET foam core, with its 100% closed-cell structure, high shear strength, and full recyclability, was rated the top-choice core material by 2026 industry evaluation (Source: Accio Market Report, 2026). XPS extruded foam excels in thermal insulation and is the classic choice for four-season RV roofs and sidewalls. PP honeycomb has an irreplaceable advantage in extreme weight-reduction scenarios, but its insulation performance is limited.

Quantitatively, the three core materials differ as follows:

• PET foam core density typically ranges 60–150 kg/m³, shear strength 1.2–2.5 MPa, water absorption < 1%, 100% recyclable;
• XPS density 30–45 kg/m³, thermal conductivity 0.024–0.034 W/m·K, water absorption < 1.5%, but lower shear strength requiring reinforcement under heavy loads;
• PP honeycomb density 30–80 kg/m³, excellent compressive strength but higher thermal conductivity (0.05+ W/m·K), unsuitable for cold-climate exterior wall insulation. 
  

On pricing, XPS starts at approximately 5/㎡, PET at 12–15.50/㎡, PP honeycomb in between (Source: Alibaba B2B Pricing Data, 2026).

Sandwich Panel Applications in RVs: Walls, Roofs, Floors, Furniture

Sandwich panel applications in RV manufacturing span the entire vehicle structure — from exterior walls and roofs to floors and interior furniture, with each position demanding different core density, face thickness, and surface treatment.

Wall panels primarily resist wind pressure, racking loads, and fastener point loads; European RV construction commonly uses 17–30mm thick PP foam or PET foam core sandwich panels with cross-ply glass-fibre skins, where 0°/90° cross-ply orientation equalises mechanical properties in both directions, allowing installation in either orientation. Roof panels must additionally carry snow distribution loads and concentrated loads from roof-mounted equipment such as solar panels, typically requiring higher core density or thicker skins for increased bending capacity.

Floor panels are a distinct category — requiring resistance to point loads from furniture legs, occupant movement, and storage weight, PP honeycomb core is preferred over foam due to its substantially higher compressive performance. On surface finish, wall panels often carry a white PET film for clean interior appearance, while floor panels use anti-skid surfaces.

BIGBAHN offers a full product line from PET foam board (core) to laminate panels (face sheets) to lightweight plywood (core/face), as a German source factory combining CNC processing and PUR flat laminating line for integrated sandwich panel production. For OEM clients, BIGBAHN can customise face sheet combinations, core density, dimensional tolerances, and surface treatment per drawings, from R&D prototyping to volume delivery all in-house.

Why Timber Frames and Aluminium Are Being Phased Out

RV manufacturers choose sandwich panels over timber frames and aluminium because sandwich panels deliver a superior strength-to-weight ratio while fundamentally eliminating the rot and corrosion problems that affect both wood and metal over time.

Timber frames absorb moisture, swell, rot, and lose structural integrity — the most documented failure mode in older caravans. Aluminium resists corrosion but adds significant dead weight, and its high thermal conductivity creates cold bridging through the wall structure.

Sandwich panel skins do not corrode or absorb water, and the foam or honeycomb core provides thermal separation between interior and exterior faces.

The commercial value of weight reduction translates directly to payload — every kilogram saved in the body structure is a kilogram available for equipment, luggage, or passenger comfort without exceeding tow vehicle limits.

For buyers considering electric tow vehicles, a lighter body extends range per charge, making weight reduction a range argument as much as a payload argument. 

Sandwich panels also reduce assembly complexity — a single panel can serve as both structural wall and finished interior surface, eliminating separate insulation layers, vapour barriers, and interior cladding. In the 2026 market trend, PET foam core sandwich panels at the heart of "100% wood-free" construction are permeating from high-end DIY expedition RVs to mainstream OEMs, with leading kit suppliers like Total Composites fully transitioning to PET foam designs (Source: Accio Market Report, 2026).

How to Choose Core and Face Materials for Different RV Positions

The first step in selection is clarifying the panel position (wall, roof, floor, furniture partition) and its corresponding load type. 

Wall panels primarily bear wind pressure and racking loads; 17–30mm thick PET foam core sandwich panels with cross-ply glass-fibre skins are the European mainstream solution, with mid-range core density (80–100 kg/m³) balancing weight and stiffness. Roof panels need additional snow and equipment concentrated load capacity — higher core density (100–150 kg/m³) or increased skin thickness is recommended.

Floor panels bearing point loads from furniture legs and occupant movement favour PP honeycomb core, whose compressive strength far exceeds foam.

Face sheet selection is equally critical. For interior faces, white PET film surfaced decorative film or laminate panels provide clean appearance and easy-clean surfaces.

For positions requiring curved shapes (roof arc transitions, curved corners), curved panels with customisable curvature enable seamless transitions. High-strength structural positions can consider GMT panels as an alternative face material. For scenarios requiring lightweight core to replace traditional wood panels, lightweight plywood offers superior strength-to-weight versus conventional plywood. Selection should also consider core-to-face bonding process — PUR flat laminating with its high-strength bond and eco-friendly PUR adhesive is the preferred process for sandwich panel lamination.

Compliance and Environment

RV sandwich panel compliance covers three dimensions: fire safety, chemical safety, and habitation health.

Under UN Economic Commission for Europe Regulation No. 118 (UN ECE R118), road vehicle interior materials must meet horizontal burn, vertical burn, and melt-drip performance limits; the regulation applies to M2 and M3 category vehicle interiors — RVs fall within this scope (Source: UNECE, Regulation No. 118, eur-lex.europa.eu). Sandwich panel face and core materials must pass ECE R118 burn testing, ensuring flame spread rate and melt-drip behaviour within safe limits.

Same-Brand Comparison: BIGBAHN Sandwich Panel Product Line

Scenario Comparison: Core Recommendation by RV Position

References 

UN ECE Regulation No. 118 — Burning behaviour of interior materials in road vehicles (Source: UNECE, 2024, https://eur-lex.europa.eu/legal-content/EN/TXT/PDF)

EN 1646-1 — Leisure accommodation vehicles: Caravans, Habitation requirements (Source: CEN, European Committee for Standardization)

Accio Market Report — Composite Panels for Campers 2026 (Source: Industry Market Analysis, 2026, accio.com)

Compoform Knowledge Base — Sandwich Panels for Caravan Walls and Roofs (Source: Compoform, 2026, compoform.com)

EU Regulation (EU) 2018/858 — Motor vehicle approval and market surveillance framework (Source: European Commission, 2018, eur-lex.europa.eu)

If you're sourcing sandwich panels for your next RV project, BIGBAHN's German source factory delivers:

• Direct factory pricing, no middleman markup

• Volume-based wholesale tiers, better pricing for larger orders

• Full OEM/ODM customization, face/core/size tailored to your needs

• All products meet ENF / FSC / CE and other international standards

Free Sample: Request Free Sample Request a Quote: Free Quote Wholesale Partnership: Become a Partner OEM Collaboration: OEM Consultation