Definition
A registered trademark of The Dow Chemical Company for extruded closed-cell polystyrene foam. In aviation, the term is commonly used (often loosely) to refer to rigid, lightweight, low-density foam used as a core material in sandwich-construction wing skins, control surfaces, bulkheads, and floats, where it provides shape and stiffness while contributing very little weight.
Plain English
A light, rigid plastic foam used inside aircraft parts to give them shape and stiffness without adding much weight.
Context Anchor
Seen in aircraft construction, repair, and homebuilt-aircraft discussions, especially when working with foam shapes, fairings, insulation, or fiberglass parts.
Derivation
A brand name coined by Dow in the 1940s, combining 'styrene' (the plastic it is made from) with 'foam.' Knowing it is a brand name explains why the same material is sometimes called polystyrene foam in technical writing.
Why Pilots Care
Foam-core structures are strong and light, but the foam can be damaged by certain fuels, solvents, and adhesives. Pilots and builders need to know what is inside the structure so they use compatible materials during repairs and refinishing.
Analogy
Think of it like a light, stiff filler inside a stronger shell. The foam gives shape and spacing, while the outer material carries most of the load.
Intuition Check
Do not assume “Styrofoam” means any white packing foam. In aviation context, it means a specific type of lightweight polystyrene foam used only where that material is suitable and approved.
Example Sentence 1
The wing was built around a Styrofoam core covered with fiberglass and epoxy.
Example Sentence 2
Technicians placed Styrofoam supports under the control surfaces to prevent damage during storage.