Stiffness and strength
Bending stiffness is set mainly by skin thickness and core depth; strength by skin strength, core shear strength and bond quality. Panel makers verify these by beam flexure testing (ASTM C393) on the actual construction.
FRP-faced sandwich panel
Fiberglass Honeycomb Panel with Aluminium Core
A fiberglass honeycomb panel is a sandwich of two thin glass-fibre reinforced plastic (FRP) skins bonded to a lightweight aluminium honeycomb core. The result is a flat, stiff, corrosion-resistant panel weighing roughly 3 – 6 kg/m², used for truck and reefer bodies, rail interiors, marine bulkheads, cleanroom walls and equipment housings. This guide explains how the panels are built, how to specify them and where their limits lie.
- Core
- 3003 or 5052 aluminium honeycomb
- Skins
- 0.5 – 1.0 mm glass/epoxy FRP
- Thickness
- About 8 – 30 mm
- Standard sheet
- 1220 × 2440 mm
What is a fiberglass honeycomb panel?
Sandwich panels work like an I-beam spread over an area. The two skins carry bending loads as tension and compression, while the core keeps them apart and carries shear. Doubling the core thickness roughly quadruples the bending stiffness for only a small increase in weight, which is why a 20 mm honeycomb panel can be as stiff as a much heavier solid sheet.
In an FRP honeycomb panel, the skins are glass-fibre fabric impregnated with epoxy (or sometimes polyester or phenolic) resin, and the core is an expanded aluminium honeycomb made from 3003 or 5052 foil. The FRP faces resist impact, scratching, moisture and chemicals and can be gel-coated, textured or coloured. The aluminium core provides high shear and compressive strength, does not absorb water and does not creep under sustained load the way polypropylene or paper cores can.
Compared with all-aluminium honeycomb panels, FRP skins give better resistance to dents, a non-conductive and thermally less conductive surface, and an easy-to-clean finish for hygienic or refrigerated spaces. Compared with panels on plastic cores, the aluminium core keeps the panel flat and dimensionally stable over a wide temperature range.
Panel construction and materials
| Layer | Typical options | Function |
|---|---|---|
| FRP skins | 0.5 – 1.0 mm glass fabric with epoxy resin; thicker or multi-ply on request | Carry bending loads, resist impact and wear, provide the finished surface |
| Adhesive | Epoxy film or liquid structural adhesive | Transfers shear between skin and core; bond quality decides panel strength |
| Honeycomb core | 3003-H18 or 5052-H18/H19 aluminium; cell size about 6, 8 or 10 mm | Separates skins, carries shear and compressive loads |
| Core thickness | About 6, 10, 15, 20 and 25 mm | Sets stiffness; total panel about 8 – 30 mm |
| Edges and inserts | Aluminium edge profiles, potted inserts, foam or solid edge fills | Provide fixing points and seal the core against moisture |
| Surface finish | Gloss or matt gel coat, textured anti-slip, coloured or primed for paint | Appearance, cleanability and grip |
Panels may be built double-sided (FRP on both faces) for self-supporting walls and floors, or single-sided, with FRP on the visible face and a thin aluminium or glass skin on the back, where the panel is bonded to a frame. 5052 cores are stronger and more corrosion resistant than 3003 and are preferred for marine and transport use; 3003 cores are economical for interior and architectural panels. Our 3003 vs 5052 core comparison explains the difference in more detail.
Typical specification and weights
Typical panel specification
- Standard size
- 1220 × 2440 mm; larger panels up to about 1500 × 4000 mm by arrangement
- Total thickness
- About 8 – 30 mm
- Thickness tolerance
- Typically ±0.2 – 0.5 mm, depending on thickness
- Length and width tolerance
- Typically ±2 mm on cut panels
- Flatness
- Typically 1.5 mm per metre or better
- Service temperature
- About −40 to +90 °C for standard epoxy systems; higher with high-Tg resins
Tolerances and temperature limits depend on resin system and construction; confirm them on the panel datasheet for your order.
Weight can be estimated from the layers. The table assumes glass/epoxy skins at about 1.9 g/cm³, aluminium core densities of 37 or 54 kg/m³ (typical of 6 mm cells in thin and medium foil gauges) and about 0.25 kg/m² of adhesive per face. Treat the results as estimates for early design.
| Core thickness (mm) | Core density (kg/m³) | Each FRP skin (mm) | Estimated weight, double-sided (kg/m²) |
|---|---|---|---|
| 10 | 54 | 0.5 | 2.9 |
| 10 | 54 | 1.0 | 4.8 |
| 15 | 54 | 1.0 | 5.1 |
| 20 | 37 | 0.5 | 3.1 |
| 20 | 54 | 1.0 | 5.4 |
| 25 | 54 | 1.0 | 5.7 |
How FRP honeycomb panels perform
Compression and point loads
The honeycomb's flatwise compressive strength (ASTM C365) decides how well floors resist wheels, feet and pallet jacks. Smaller cells and heavier foil raise it.
Moisture
Neither the aluminium core nor cured epoxy absorbs significant water, but edges must be sealed so water cannot travel through the cells. Unsealed cut edges are the most common cause of panel failure outdoors.
Corrosion
FRP skins do not corrode. 5052 cores resist humidity and salt spray well; for marine use specify corrosion-protected core foil and sealed edges.
Thermal behaviour
FRP faces conduct heat far less than aluminium skins. For insulated reefer bodies, honeycomb panels are combined with foam layers because the open aluminium core itself is not an insulator.
Long-term load
Aluminium honeycomb does not creep at normal service temperatures, so floors and shelves keep their flatness under sustained loads.
Fire performance: what to check
Fire is where FRP panels need the most care. The aluminium core is non-combustible, but epoxy and polyester resins burn and produce smoke. Standard FRP honeycomb panels are therefore not suitable where non-combustible materials are required, for example on many building facades. Flame-retardant resin systems and phenolic skins improve performance substantially, and the right test depends on the application:
| Application | Typical fire standard | Note |
|---|---|---|
| Railway vehicles (Europe) | EN 45545-2 | Hazard levels HL1 – HL3; flame-retardant or phenolic skins usually needed |
| Ships | IMO FTP Code (2010) | Surface flammability, smoke and toxicity for interior linings and bulkheads |
| Buildings (Europe) | EN 13501-1 reaction-to-fire classes | Facade and escape-route rules may exclude combustible panels |
| Buildings (US) | ASTM E84 flame spread and smoke index | Interior finish classes A, B, C |
| Aircraft interiors | 14 CFR 25.853 | Normally phenolic-glass skins on aramid or aluminium cores |
Always ask for a fire test report on the exact construction (skin, resin, adhesive, core and thickness). A report for a different build does not transfer.
Cutting, fixing and edge sealing
- CuttingCut with fine-tooth carbide or diamond saws, or CNC routers with dust extraction. Glass-fibre dust is abrasive and an irritant, so use extraction and protective equipment.
- Inserts and fixingsThrough-bolts crush the core unless the hole is reinforced. Use potted inserts (resin-filled core around a threaded insert) or solid edge and hardpoint fills where fixings carry load.
- Edge closureSeal every cut edge with an aluminium U-profile, edge filler resin or sealant so moisture cannot enter the cells.
- Joining panelsJoin with extruded aluminium H-profiles, corner profiles, or bonded splines. Structural adhesives spread load better than discrete fasteners.
- Grooving and foldingV-grooving the back skin and core lets panels be folded into boxes and corners; the groove is then bonded and sealed.
For more on joining methods and their effect on panel strength, see honeycomb core joining methods.
Aluminium honeycomb versus other cores under FRP skins
| Core | Strength and stiffness | Creep and temperature | Moisture | Typical use |
|---|---|---|---|---|
| Aluminium honeycomb | High shear and compressive strength for its weight | No creep; stable over a wide range | Does not absorb water; edges must be sealed | Vehicle floors and walls, marine, equipment |
| Polypropylene honeycomb | Much lower than aluminium at similar density | Softens with heat, can creep | Does not absorb water | Low-cost panels, light partitions |
| Paper / kraft honeycomb | Low | Creeps under load | Absorbs water and loses strength | Doors, furniture, dry interiors |
| PET or PVC foam | Moderate; continuous bond area | Some grades creep at high temperature | Closed-cell, low absorption | Marine hulls, wind blades, insulated bodies |
| Aramid honeycomb | High; good fatigue and impact | Good to elevated temperatures | Low absorption | Aircraft interiors and structures |
Metline supplies the aluminium honeycomb core and aluminium-cored panels. For a direct comparison with aramid cores, read aluminium vs aramid honeycomb core.
Where fiberglass honeycomb panels are used
- Truck, van and reefer bodies: side walls, roofs and floors where low weight raises payload and FRP faces stand up to loading damage
- Rail interiors: wall linings, ceilings, partitions and floors built to EN 45545-2 fire requirements
- Marine: bulkheads, cabin linings, deck coverings and furniture bases in humid, salty environments
- Modular and mobile buildings: wall and roof panels for site cabins, shelters and equipment containers
- Cleanrooms and food plants: washable wall and ceiling panels with smooth gel-coat faces
- Industrial equipment: housings, guards, maintenance platforms and access panels
A typical example is a delivery-van side wall: a 20 mm panel with 1 mm FRP skins on a 5052 core weighs a little over 5 kg/m², takes rivnut or bonded fixings at potted hardpoints, and gives a smooth face for graphics.
How to specify and order
- Size and thicknessPanel dimensions, total thickness and quantity; cut-to-size or full sheets.
- Skins and finishSkin thickness, single- or double-sided, colour and surface texture.
- CoreAlloy (3003 or 5052), cell size and density, or the required compressive and shear performance.
- Performance and fireLoads, temperature range and the fire standard that applies.
- Processing and deliveryEdge closure, inserts, grooving; destination and terms (EXW, FOB, CIF or DAP). Panels ship flat on pallets with protective film and edge guards.
References and standards
- ASTM C393/C393M – Core Shear Properties of Sandwich Constructions by Beam Flexure
- ASTM C365/C365M – Flatwise Compressive Properties of Sandwich Cores
- ASTM C297/C297M – Flatwise Tensile Strength of Sandwich Constructions
- EN 45545-2 – Railway applications: fire protection on railway vehicles, requirements for fire behaviour of materials
- EN 13501-1 – Fire classification of construction products and building elements
Fiberglass honeycomb panel: FAQ
What is the core of a fiberglass honeycomb panel?
In the panels described here the core is expanded aluminium honeycomb in 3003 or 5052 alloy, typically with 6 – 10 mm cells. Some panels on the market use polypropylene, paper or aramid cores, which behave differently in strength, creep and moisture.
How much does an FRP aluminium honeycomb panel weigh?
Roughly 3 – 6 kg/m² for common builds. A 20 mm panel with 1 mm glass/epoxy skins on a medium-density aluminium core weighs about 5.4 kg/m².
Can fiberglass honeycomb panels be used outdoors?
Yes, provided all edges are sealed and the gel coat or surface finish is UV resistant. FRP skins and aluminium cores do not corrode, but water entering through open cut edges must be prevented.
Are FRP honeycomb panels fireproof?
No. The aluminium core does not burn, but standard resins are combustible. Flame-retardant or phenolic skins can meet rail, marine and many interior fire standards; check the test report for the exact construction and application.
Is a fiberglass panel better than an aluminium-skinned honeycomb panel?
It depends on the use. FRP skins resist dents and chemicals and give a washable, insulating surface. Aluminium skins are stiffer for the same thickness, non-combustible as a face material, and easier to coat for architectural finishes.
Can panels be cut and drilled on site?
Yes, with carbide or diamond tools and dust extraction. Seal cut edges afterwards and use potted inserts or reinforced hardpoints for any fixing that carries load.
Planning an FRP honeycomb panel project?
Send the size, thickness, skin and core preferences, fire requirement and quantity. We will propose a construction and delivered price.
