Definition
A layer of finely woven fabric, often nylon or polyester, applied as the outermost ply during the layup of a fiberglass or composite structure. After the resin cures, the peel ply is torn away, leaving a clean, slightly textured surface that is ready for bonding or further lamination without additional sanding.
Plain English
A sacrificial cloth laid on top of a wet composite layup. Once the part hardens, you peel the cloth off, and it leaves behind a clean, rough-textured surface that is perfect for gluing or adding more layers later.
Context Anchor
Seen in composite aircraft construction and repairs, especially when a repaired surface will need another layer, sealant, or finish after it cures.
Derivation
The name is descriptive: it is a 'ply' (a layer of fabric) that is meant to be 'peeled' off after the resin cures. 'Ply' comes from the Latin plicare, meaning 'to fold or layer.'
Why Pilots Care
Creates the textured surface needed for strong secondary bonds in composite repairs, which is essential for maintaining structural integrity on many modern aircraft.
Intuition Check
Do not think of peel ply as part of the finished aircraft structure. It is usually a temporary process layer that is removed after curing.
Example Sentence 1
After the fiberglass patch cured overnight, the technician pulled off the peel ply to reveal a clean bonding surface for the next layer.
Example Sentence 2
Once the resin had cured, the peel ply was removed to expose a surface ready for the next bonding step.