Sandwich Core Materials
A sandwich core is the light middle of a stiff panel: it holds two thin skins apart so the panel gains bending stiffness with the cube of its thickness while adding almost no weight — doubling the thickness of a skin with core makes it about seven times stiffer for 3 % more mass. Cores are closed-cell polymer foams at 40–250 kg/m³ (cross-linked and linear PVC, PET, SAN, PMI, PU, PIR, XPS and EPS), end-grain balsa at 100–250 kg/m³, and honeycomb in Nomex aramid, aluminum, glass-phenolic, polypropylene, stainless or titanium at 30–130 kg/m³. The core carries the shear and the compression under the skins, so shear strength and modulus per unit density, process temperature and resin compatibility are what separate them.
Popular sandwich core grades
Compare in the explorer| Grade | Yield, MPa | Tensile, MPa | Density, g/cm³ | Machinability | Best for |
|---|---|---|---|---|---|
| Cross-linked PVC Foam Core | — | 3 | 0.08 | Excellent | General structural foam for hulls and panels |
| PET Foam Core | — | 2 | 0.1 | Excellent | Recyclable infused panels and blade shells |
| PMI Foam Core (Rohacell) | — | 2 | 0.08 | Excellent | Autoclave prepreg cores at 130–180 °C |
| End-Grain Balsa Core | — | 13 | 0.15 | Excellent | Highest shear strength per weight; fire performance |
| Nomex Honeycomb (HRH-10) | — | 3 | 0.05 | Fair | Aircraft interiors, radomes, racing panels |
| 5052-H39 Aluminum Honeycomb | 1 | 3 | 0.05 | Fair | Stiffest light flat panels and tooling |
| SAN Foam Core | — | 2 | 0.08 | Excellent | Tough marine cores that survive impact |
All 21 sandwich core grades
- 5052-H39 Aluminum Honeycomb
- 5056 Aluminum Honeycomb
- Aramid Fiber Honeycomb (HRH-49)
- Cork Composite Core
- Cross-linked PVC Foam Core
- End-Grain Balsa Core
- EPS Foam Core
- Fiberglass/Phenolic Honeycomb (HRP)
- Linear PVC Foam Core
- Nomex Honeycomb (HRH-10)
- Nomex Honeycomb Core
- PET Foam Core
- PMI Foam Core (Rohacell)
- Polyisocyanurate (PIR) Foam Core
- Polypropylene Honeycomb Core
- Rigid Polyurethane Foam Core
- SAN Foam Core
- Stainless Steel Honeycomb Core
- Syntactic Foam Core
- Titanium Honeycomb Core
- XPS Foam Core
Choose sandwich cores for
Boat hulls, decks and bulkheads; wind-turbine blade shells and shear webs; aircraft floors, interiors, fairings and radomes; race-car body panels and splitters; flat structural panels, tables and enclosures that must be stiff and light; composite tooling and layup molds; and any panel where a solid laminate would be heavy and a stiffened metal sheet would be complex.
Look elsewhere when
The panel takes concentrated loads, bolts or edge fixings without inserts and potting (cores crush — design the hard points), it will be machined into a solid 3D part rather than a panel, it runs above the core limit (about 80 °C for PVC, 130 °C for PET and Nomex, 180 °C for PMI and aluminum), it must hold vacuum or pressure without sealed edges, water can reach the core (balsa rots, open honeycomb fills), or a thick monolithic Carbon Fiber or G10 plate is simply easier for a small machined bracket.
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Sandwich core by application
- Boat hulls and decks
- Cross-linked PVC Foam Core or SAN Foam Core at 80–130 kg/m³ for hull sides and decks, Linear PVC Foam Core in slamming zones, End-Grain Balsa Core under fittings and in floors where compression strength counts.
- Aerospace and racing panels
- Nomex Honeycomb (HRH-10) and Aramid Fiber Honeycomb (HRH-49) for interiors, radomes and floor panels; PMI Foam Core (Rohacell) where the core must be machined to shape and cured under autoclave pressure.
- Flat stiff panels and tooling
- 5052-H39 Aluminum Honeycomb or 5056 Aluminum Honeycomb between aluminum or glass skins for optical tables, machine covers and layup tools; Polypropylene Honeycomb Core for low-cost thermoplastic panels.
- Buoyancy and insulation
- Syntactic Foam Core for subsea floats and pressure-tolerant fairings; Polyisocyanurate (PIR) Foam Core, Rigid Polyurethane Foam Core and XPS Foam Core for insulated panels where structure is secondary.
Working with sandwich core
- Cutting and machining
- Foam cores CNC-route with sharp single-flute or burr tools at high speed and low pressure, hot-wire cut in XPS and EPS, and thermoform (PVC, PET, SAN) at 100–150 °C to double curvature; grid-scored and perforated sheet drapes onto simple curves without heat. Honeycomb is band-sawn, routed with a valve-stem cutter or ultrasonically cut, and expanded aluminum core is held on vacuum or frozen in ice to machine. Balsa cuts like wood and needs sealing.
- Bonding and layup
- The skin-to-core bond decides the panel: use a film adhesive or a filled bond coat, and for resin infusion choose a core with flow channels or grooves. Polyester and vinyl ester resins dissolve EPS and attack XPS — use epoxy — while PVC, PET, SAN and balsa take any resin. PMI and Nomex are cured with prepreg under vacuum or autoclave pressure; aluminum honeycomb bonds with epoxy film and must be corrosion-treated and isolated from carbon skins.
- Design rules
- Size the core for shear and the skins for bending; put a potted insert, a solid laminate island or a high-density core plug under every bolt, hinge and bracket, and taper the core to a solid edge rather than leaving it exposed. Keep water out: seal cut edges, and remember that open honeycomb cells pump moisture in and out with pressure changes.
- Temperature and environment
- PVC foams soften around 80 °C and are not for hot-cured prepreg; PET and SAN take about 130–150 °C in process; PMI, Nomex and aluminum survive 180 °C autoclave cycles. Balsa must be dry (below 12 % moisture) and sealed or it rots; aluminum honeycomb corrodes if the skins leak; EPS and XPS creep under sustained load and are not structural cores.
Other composite series
Sandwich Core Materials — frequently asked
What is sandwich core?
A sandwich core is the light middle of a stiff panel: it holds two thin skins apart so the panel gains bending stiffness with the cube of its thickness while adding almost no weight — doubling the thickness of a skin with core makes it about seven times stiffer for 3 % more mass. Cores are closed-cell polymer foams at 40–250 kg/m³ (cross-linked and linear PVC, PET, SAN, PMI, PU, PIR, XPS and EPS), end-grain balsa at 100–250 kg/m³, and honeycomb in Nomex aramid, aluminum, glass-phenolic, polypropylene, stainless or titanium at 30–130 kg/m³. The core carries the shear and the compression under the skins, so shear strength and modulus per unit density, process temperature and resin compatibility are what separate them.
Which grade of sandwich core should I use?
Cross-linked PVC Foam Core for boat hulls, decks and general structural panels — the best-balanced shear strength, fatigue and resin compatibility at 60–200 kg/m³, and it thermoforms to curves. Linear PVC Foam Core when impact and ductility matter more than stiffness. PET Foam Core as the recyclable, higher-process-temperature alternative for wind blades and infused panels, accepting lower fatigue life; SAN Foam Core for tough marine laminates that see repeated impact. PMI Foam Core (Rohacell) where the panel is cured in an autoclave with prepreg at 130–180 °C — the aerospace foam, fine-celled and stable under pressure. End-Grain Balsa Core for the highest shear and compressive strength per weight and good fire performance, sealed against water. Nomex Honeycomb (HRH-10) for aircraft interiors, radomes and racing panels; 5052-H39 Aluminum Honeycomb for the stiffest, lightest flat panels and tooling, isolated from carbon skins. Polypropylene Honeycomb Core for low-cost thermoplastic panels, Syntactic Foam Core for deep-water buoyancy, and XPS Foam Core or EPS Foam Core only for insulation panels and plugs, with epoxy rather than polyester resin.
Which grade of sandwich core is the strongest?
5056 Aluminum Honeycomb has the highest yield strength in the series at 3 MPa; 5052-H39 Aluminum Honeycomb follows at 1 MPa. Values are for each grade's default condition.
Which grade of sandwich core is easiest to machine?
Polyisocyanurate (PIR) Foam Core (machinability excellent, 93/100), then End-Grain Balsa Core (92/100).
PVC, PET or balsa core for a boat?
Cross-linked PVC Foam Core is the marine default: good shear strength and fatigue, closed cells that will not wick water, compatible with every resin, thermoformable and available in 60–200 kg/m³. PET Foam Core is a little heavier for the same shear strength and fatigues faster, but it is recyclable, tolerates hotter processing and is preferred by builders infusing large panels. End-Grain Balsa Core has the highest shear and compressive strength per weight and the best fire and impact behaviour, at 100–250 kg/m³, but it absorbs resin, adds weight and rots if a fitting leaks — so it goes under hardware and in decks, not in hull sides.
Foam or honeycomb core?
Honeycomb gives the highest stiffness and strength per weight — Nomex Honeycomb (HRH-10) at 48 kg/m³ has roughly the shear modulus of a foam two to three times as dense — which is why aircraft floors and racing panels use it. Foam wins on everything practical: it bonds over its whole face rather than on cell edges, machines and thermoforms to curves, tolerates vacuum infusion, does not fill with water through a skin crack, and costs a fraction. Use honeycomb for flat, weight-critical, autoclave-cured panels; foam for curved, infused or wet-laid parts and anything that lives near water.