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Core Materials in Sandwich Composites: Foam vs Honeycomb

1 May 2026
4 min read

Why Core Material Matters in Sandwich Composites

A sandwich composite achieves its structural efficiency through the same principle as an I-beam: place stiff, strong faces far apart, separated by a lightweight core that resists shear and prevents the faces from buckling. The core is not a filler — it is a structural element. Its mechanical properties, density, thermal behaviour, and compatibility with your manufacturing process directly determine whether your sandwich structure performs as designed.

Structural Foam Cores

  • PVC foam (Divinycell, Airex C70): The most widely used foam core. Excellent balance of shear strength, elongation, and price. Available in densities from 40 to 200 kg/m³. Compatible with all infusion and prepreg processes. Widely used in marine, wind energy, and transportation.
  • PET foam (Airex T90, Corecell T): Thermoplastic — can be post-formed, good chemical resistance, fully recyclable. Growing in wind blades and automotive applications.
  • PMI foam (Rohacell): Polymethacrylimide. The highest-performance foam core. Excellent temperature resistance (up to 220°C for some grades). Standard for aerospace parts processed in autoclave. Significantly more expensive than PVC.
  • SAN foam (Corecell A-Series): High toughness and elongation — resistant to impact and fatigue. Used in marine racing hulls and high-dynamic loading applications.

Foam Core Advantages

  • Easily shaped to complex curves by thermoforming or machining
  • Compatible with vacuum infusion
  • Closed-cell construction resists water ingress
  • Lower tooling cost for curved structures
  • Repairs are straightforward

Honeycomb Cores

  • Nomex honeycomb (aramid paper): The aerospace and defence standard. Lightweight, flame-retardant, excellent specific stiffness. Used in aircraft floors, interior panels, fairings, and satellite structures. Requires film adhesive and autoclave or press bonding.
  • Aluminium honeycomb: Higher shear modulus than Nomex. Used where in-plane stiffness is critical. Prone to galvanic corrosion with carbon fiber if not managed carefully.
  • Thermoplastic honeycomb (PP, PET): Lower cost, good specific properties, can be thermoformed. Used in automotive and transportation applications.

Honeycomb Core Advantages

  • Higher stiffness-to-weight ratio than foam at equivalent areal weight
  • Very low density achievable — 16–80 kg/m³ for Nomex
  • Excellent out-of-plane compressive strength
  • Dimensional stability under thermal cycling

Direct Comparison: When to Choose Each

  • Choose foam when: your process is vacuum infusion; the structure has complex curvature; cost is a significant constraint; water ingress resistance is required without additional sealing
  • Choose honeycomb when: maximum stiffness-to-weight is required; the process is autoclave prepreg; panel geometry is relatively flat; aerospace or defence qualification standards apply

For technically demanding applications — aerospace, motorsport, high-performance marine — GLB Composites can provide material datasheets, density options, and process compatibility data to support your sandwich structure design.