Definition
A lightweight cellular material made by causing a plastic resin to foam during manufacture, producing a structure of small gas-filled cells trapped within the cured plastic. Used in aircraft as core material in sandwich panels, as thermal and acoustic insulation, and as flotation filler.
Plain English
A foam-like plastic full of tiny gas bubbles, which makes it very light and a good insulator. It is used inside aircraft panels, behind cabin walls, and in places where weight needs to be kept low.
Context Anchor
Seen in aircraft maintenance, repair, and construction discussions involving foam materials, interior parts, insulation, flotation, or lightweight panel construction.
Derivation
‘Expanded’ comes from the Latin expandere, meaning to spread out. The plastic is literally spread out by gas during manufacture, swelling from a small amount of resin into a much larger, lighter volume of foam.
Why Pilots Care
Expanded plastic cores are common in floor panels, bulkheads, and fairings. Damage to these areas often involves a thin skin over a foam core, and the foam itself can absorb water or fuel if the skin is breached, adding hidden weight and corrosion risk.
Analogy
Expanded plastic is like packing foam compared with a solid plastic block: both are plastic, but the foam has many tiny spaces inside, so it is much lighter.
Intuition Check
Expanded does not just mean the plastic was stretched or made larger. Here it means the plastic has a foam-like internal structure with many tiny gas-filled spaces.
Example Sentence 1
The cabin floor panel uses an expanded plastic core sandwiched between two thin fiberglass skins to keep weight low.
Example Sentence 2
Cabin side panels used expanded plastic for both soundproofing and reduced weight.